Hi everyone I'm a first time mum and my litt...

Hi everyone I'm a first time mum and my little girl is now three weeks old. I've been exclusively breastfeeding, although I've been using a nipple shield since week two due to cracked and bleeding nipples (have been trying to latch without it the last few days but have been unsuccessful so far). The last few days she's been very fussy, wanting to constantly feed but also constantly pulling off. I've had to offer both breasts during each feed but she never seems satisfied. For the most part she won't sleep for more than half an hour to an hour without being cuddled and the longest she's slept for a few days is three hours. She was born at 3.5kg, dropped to 3.4kg to 3.2kg then back up to 3.3kg in the first week and a half to 2 weeks. She's staying around the 3.3kg mark and I'm really concerned she hasn't regained her birth weight. She's also only been having about 3-4 proper wet nappies in 24hrs. Last night after her bath I offered both breasts and when she became too fussy I offered her 50ml of formula and she guzzled almost half of it in about 1 minute. I'm wondering if I'm maybe not producing enough milk? I don't know whether I should continue exclusively breastfeeding and see how she goes, just offer her formula if she continues to be fussy after trying both breasts or switch to formula completely. The whole thing is really stressing me out (which obviously won't help with my milk) and I'm so conflicted because I never wanted to use formula. Any advice would be greatly appreciated.