Please help! 7 week old latching then unlatching then refusing to latch back on breast!

i was wondering if someone could help?  my baby is 7 weeks old today and has been breastfeeding really well so far. She’s gained weight fine and hasn’t had any problems until this weekend! She was having greenish nappies and they were mucusy but look like today they have gone back to normal. But all weekend she will latch onto my breast for a few minutes then unlatch and attempt to relatch but wiggles her head, gets frustrated and cries. I make sure to burp her and offer her the other breast, but it still happens And she won’t latch again. I feel like my milk supply is suffering and becoming low as they never get full anymore and are starting to feel emptier than they have been and she’s not getting enough. I’m so tempted to switch to bottle but I’ll feel so bad if I do, it’s just been a really tough weekend with it? Has anyone got any ideas or suggestions? I’m getting her weighed again Wednesday to see if she’s lost weight, if she has and things haven’t improved I’m turning to formula but really don’t want too