Thank you for your support everyone, somehow knowing that's my baby is not the only one like this helps me cope with all this. Everyone I know irl, including parents etc, think my baby is broken or spoilt as theirs never did this.
I ended up waking DH up and he took the baby for a couple of hours but had to then go to work. So I got little bit of rest.
In terms of naps, he normally has a 3h nap in the morning until lunchtime, a 1-2h nap mid-afternoon and a 30min-1h in the early evening. I struggle getting him to nap any more, he doesn't really go to sleep until he's been awake for at least 1.5-2hrs. Bedtime is at around 8pm and he used to do a 4-6h stretch and then 2h stretches until 7-8am.
In the last few days naps definitely got more difficult, he's clearly tired but fights them and wakes up earlier, eg 3h morning nap was a 2h yesterday and mid-afternoon one was only 3min. I couldn't get him back to sleep once he woke up.
As I put above, he only sleeps on my chest in the daytime. I usually need to walk around to get him to sleep so I put him in a sling and go for long walks. I wish he slept in the pushchair or in the car but he doesn't, he just screams his lungs out until I pick him up. It's absolutely ridiculous but I've come to terms with having him attached to me in the sling in the daytime. But obviously I can't do this round the clock.
He also hates being with anyone other than me. He doesn't settle with my DH or MIL (who lives over 2hs away but comes once a week to help) and screams within minutes of being left with anyone other than me. So I have to settle him and pass over gently, then he might stay asleep if we're lucky. Sometimes we have to do this 2, 3, 4 times before it's successful. Sometimes it doesn't work at all and he wakes up, sees that I'm not there and screams. Then calms down instantly when I take him. HV just said that I have a clingy baby.
So all of his sleep got worse recently. Perhaps there is something medical going on, I will check his temperature. He doesn't seem to be in pain though, he doesn't cry more than usual. Just whines asking to be picked up and is happy when I do. He did cry more yesterday early evening but I think it was from being overtired. I really doubt that he's getting enough sleep at the moment. It feels a bit silly calling GP and asking for an appointment for a baby with no symptoms other than being extra clingy..
I usually wait 20 mins before putting him down, but tried longer (up to 1.5h) in the last few days with no change. Perfectly still when first put down but wake up 20-30 mins later.