@gg321 I had the same problem as you with my first (10 lb 4 baby, static weight for ages, lots of pressure to top up feed), and now having similar issues with my second (9 lb 4).
With my first it turned out it was tongue tie - midwives are not specifically trained to recognise or diagnose tongue tie, you need to see an infant feeding specialist or a tongue tie practitioner to get it properly diagnosed. If possible, go private (the NHS waiting list for tongue tie division is ridiculous). There's a website with contact details for private tongue tie practitioners, Google it and it should come up. It made the world of difference with my first.
However with my second I don't think it's tongue tie, I think it's just that he was born a big baby and isn't meant to be that big. Midwives take no account of the fact that if you and your partner aren't naturally large people that your baby probably won't be either. It is very common for large babies to "trend down" after birth, but the midwives guidelines on birth weight create all this unnecessary pressure around regaining weight within a certain timeframe which doesn't work well with large, breastfed babies.
As a previous poster said, as long as baby is having plenty of wet and dirty nappies, is otherwise alert and happy, then you can refuse to do weigh ins and top ups. I wish I'd known this first time round as I ended up pumping and topping up for months and nearly lost my sanity, but my first went from 98th centile to 50th and happily stayed there. She's now a very robust 2.5 year old.
Things to help with pumping: look up "power pumping" - it's a method that attempts to replicate cluster feeding and is good at upping your supply and getting lots of milk without having to be tied to pumps for hours. Get a medical grade double pump with a pumping bra so that you're hands are free. I used the spectre S1 and can highly recommend it in terms of how quickly and efficiently it extracted milk. When pumping throughout the day you can continue to use the same bottles for 6 hours without washing them, just put them in the fridge between uses - this saves loads of hassle with washing up. Oh and they don't need sterilising, just washing with hot soapy water. Also, I pumped for approx 5 minutes before feeding, this meant that I got the easily accessible milk with the pump while baby (who is much better at getting milk out) was able to get what I couldn't after I'd pumped. It also meant baby has the fattier milk that comes through at the end of a feed, rather than the watery milk at the beginning.
Other helpful things: breast compressions before and during feeds/pumping, lots of skin to skin, keeping well hydrated, eating oats, try fenugreek capsules, don't restrict your calorie intake, avoid alcohol and peppermint tea.
Oh and don't use nipple shields unless you have bad nipple trauma or baby can only latch that way, they really reduce supply. Feel free to PM me if you have any questions!