Wish we'd never started

Hi, We started potty training our son at 21 month which i know is early. He was showing all the signs of being ready and has been early with every other milestone so we thought we'd give it a try. We went properly nappy free and no pull ups. For a few weeks we had a few accidents but they got less. We would go for a couple of days with him doing well and then have a bad day. Then i suddenly noticed that he had been completely dry for 5 days in a row and thought we had cracked it! But this week he has regressed completely! He's weeing and pooing everywhere like he isn't potty trained at all. Part of me wants to just give up, but he won't hear of wearing nappies now! It started when my mum came and looked after him for 2 days while I was at work instead of usual childcare. Could this have really messed him up this much? She left weds and today is Friday and he's still the same. He is also teething. .. could that be it? Any advice? I'm feeling really stressed and finding it difficult as I'm pregnant too and find myself getting stressed more easily! I really wish we'd never started! !