If you've tried absolutely everything for the naps and are rocking for 20 minutes plus whilst baby is fidgeting and crying, you are well within your rights to try putting baby down to sleep freshly fed and nappy changed and leave for 15 minutes. You may discover you have a baby who is developing into wanting to be left alone to fall asleep. It is just another method to try if all else is failing. If you know bubba is overtired and is fighting sleep try this starting on a Friday evening for bed time then partner can provide support, if it works, you can follow through next day for naps when baby is throwing you sleepy signals. If you don't have a baby that's throwing you signs, go with an hour after wake-up in the morning as it's the easiest time usually for baby to take a nap (I find they fight it more as the day goes on). If baby falls asleep within 20 minutes alone after a cuddle and feed (contrary to popular feed play sleep, I find bottle then down stopped my baby fighting sleep as full belly must have helped), you can try again for the next nap, probably an hour and a half after waking. This MAY help, this may also not work for your little one. Just a suggestion as if you feel you are doing everything and it is working less and less and getting more difficult it is always wise to try something new instead of struggling with old methods. They change so much and so quickly, something that worked a week ago they may have decided to phase out and they don't like it anymore.
I have a 6 month old and 2 to 3 months old was when shit hit the fan for me and I was struggling, baby was wiggling in my arms suddenly unable to be rocked and didn't fancy naps how I'd managed previously. Sleep is an absolute dream now and mine does 6:30pm to 5ish am, small feed back down till 7am. Then naps at around 9, 12, and 3pm and bedtime routine begins at 6. I know I may have it easy but I also worked on his naps around the age your bubba is because I couldn't take rocking anymore and he suddenly started fighting it.
If it helps and you have the ability to go round grandparents and ask them to shush and pat bubba to sleep for a nap whilst you relax, do it. It may just kickstart LOs ability to fall asleep without you having to feel guilty if you are inclined that way.
Also from 2 and a half ISH months I started holding his hand and singing twinkle twinkle, dummy came into play etc to save my arms from constant rocking.
I'm sure you're doing great and even at 6 months it gets much better, and I'm sure our reward will be clear over the next few years. Just consider different methods to help you cope, I'm suddenly on my own as partner has issues causing us to split and him barely seeing my baby over the past 2 months so I can relate with the having to do everything.
Some babies just don't sleep, but if yours is in the roughly 60% of babies that are maleable (with 20 being easy already and 20 being difficult colicky babies, read this somewhere, not pulling out my arse), you should be able to get naps down with a little bit of work. And to the user questioning why sleep training comes into play, if you are struggling with bubba and at wits end, being able to put them down for a nap and then they drift off themselves as opposed to hours of your day rocking, it's a game changer. Changed my experience completely and me and my one are much better off for it.
You can do it. :) feel free to message if you are interested in trying anything I've suggested and I will give a more in depth explanation of what I've done.
Also I was adamant I wanted to breast feed and tried so hard but baby decided at 4 ish months he wouldn't feed properly and barely latched on after growing amazingly at the beginning of his life, and wasn't putting on weight. I moved to formula with regular breastfeeds 4x a day but 3 formula bottles a day and now I'm pretty much entirely feeding baby formula and weening with him bf morning and pre bed. This helped me and I was very strict on "I HAVE to breastfeed". Knowing he is getting my antibodies from the few bfs but I don't need to manically pump or surrender my boobs has also helped mentally.
Ranting on now but a dummy also helped with the putting down to sleep without rocking. And my lo is barely attached to it, will only have it immediately after bottle to stop tears (for about 2 mins then spat out) and before naps where he spits it out before actually falling asleep. I was also against dummy's for whatever reason but they have helped so much as provide that little bit of comfort for baby when you leave the room.
Lastly be easy on yourself. It will get better and it's difficult feeling as if you are doing everything but your partner may not realise the gravity of stuff you're dealing with day to day. Make the most of your evenings if baby insists on refusing naps and wear baby around the house to get some bits down or plop on chair and allow yourself some time to focus on doing what YOU need to do because you need to feel at least somewhat complete to be able to mother a tiny human, and if that means baby fed nappy changed crying for ten minutes on play mat, it usually has to be done. Calm yourself knowing you will be cuddling baby very soon and they know no other communication from crying. You got this