Firstly congratulations 
Hi, it sounds like you’re doing great- breastfed babies do lose a small amount of weight at the start then gain it again once breastfeeding has been properly established - very normal.
Re: the lack of feeding routine, again this is normal and is called cluster feeding - basically it’s kind of all over the shop in terms of how long they’re feeding/sucking for and the length of times between feeds - not long really as they are sucking to stimulate milk production so it will feel like they’re stuck on you continually for about a week Iirc (sorry it’s been nearly 1.5 years since I bf a newborn so timings are abit hazy). Do you have good support at home? I was lucky I could basically bed down with my babies when they were this small, set myself up with plenty of drinks, snacks and books/box sets and let them do their thing. Although yes there were plenty of times I needed someone else to hold them for 20 mins just to give me a physical break.
Also expressing isn’t a true reflection of how much your baby is getting as it’s not the same as a baby feeding which will manage to get more than you can express which is partly down to the oxytocin’s - that pins and needles type sensation called ‘let down’ which is when your body responds to your baby. Again it’s been a while so worth looking it up but there are helpful techniques to harness this - focus looking at and smelling your baby will help.
Has your midwife arranged for a breastfeeding consultant to come visit you?
What helped me enormously was to search terms like breastfeeding newborn baby and cluster feeding on MN - there’s loads of threads and made me feel less lonely when I realised how common it was to struggle to establish breastfeeding.
Also do consider contacting La Leche League (voluntary breastfeeding Advice group)
I’ll not kid you that it isn’t hard the first month or so, there’s been plenty of times I’ve cried and doubted myself, that my breasts and nipples hurt so much, that I felt so overwhelmed with this little life that 100% depended on me. There is no right or wrong way to feed a baby, I’m giving you my experience but what you decide is right for you and your baby is totally your call. I found the early days so so hard, I wish I could offer you more than an online hand hold 