Potty Training Advice Needed

Potty training advice, please. My son is 2 1/2. We started the potty training journey around 3 weeks ago. I expected it to be super difficult because he is very hard headed, but it was honestly like a dream. I basically said that we are using the potty now and he just did. Pee and poop from day one, one accident. He has even been great about peeing in public (unless he sees or hears someone use the scary hand dryers). It couldn’t be that easy, right? Right. Fast forward to Saturday. We had been on the go a lot the past few days and he asked to go poop. A bit panicked. When he went he was very constipated, which doesn’t ever happen to my fruit loving boy. It hurt him pretty good. Well now we have yet to poop in the potty since. He is holding it. I can tell he needs to go. Once he accidentally went on the floor. Now he is asking to go outside. So Saturday- constipated, Sunday- held it, Monday-constipated again/floor accident, today- holding it. I know he needs to go, but he has pretty good control. We are pounding the juice and fruit. This evening he wouldn’t even try to pee because I think he knew he would end up going. I tried to make him go. Fits ensued, so I’ve probably messed everything up now. I need expert advice. Thanks for reading, and thanks in advance!