@apa I haven’t had time to read other people comments, but as your baby is still below their birth weight at 5 weeks my expectation would be that you need to supplement with formula immediately and then figure the rest out.
Little babies can have enough to be hydrated but not gaining weight and at this age it is critical that she gins weight along the expected curve. Her little brain and body need all the help they can get to grow.
You’re not “giving up” on anything except for the idea that you had of exclusively breastfeeding. It sounds like you’ve had a rough time so far, so you already know that every really great plan and theory you had on how you would parent and how everything would work goes out the window and you adjust and make it work!
You can still breastfeed and your baby will still have all the benefits of breastmilk while you combo feed, and you can give yourself some time and space to figure out why she isn’t gaining weight (maybe she’s still under the weather, maybe your supply is a bit low, maybe she has latch issues and isn’t emptying the breast efficiently, maybe she has tummy issues of some sort and you need to look at diet etc)
I had intended to EBF but our daughter was HOPELESS at breastfeeding so I ended up combo feeding and triple feeding to get my supply up while we practiced…I actually ended up preferring to combo feed and did it for 13 months, but many many people go back to breastfeeding only once they have ironed out the difficulties of breastfeeding.