What is going on!?

I was feeling so hopeful with sleep training our almost 5 month old last week. It was going well for 3-4 days then suddenly the last 2 nights she’s been screaming every 2 hours like she’s actually in pain and so hard to soothe. Before she only mildly fussed and she put herself back down within 15 minutes. We did recently introduce oatmeal and bananas. Could it be that? Gas? Teething? I don’t know but now I feel so discouraged like everything is derailed. I normally don’t mind her fussing it out but I don’t feel I shouldn’t ignore her when it sounds like she’s in true pain. Anyone else experience something like this? Maybe from introducing solids? Or is she just protesting more? Help 😵‍💫