Hi - I'm not sure I have an answer but I had a similar experience. My son started potty training at 3 yrs. old. It went well until he got gastrointeritis and had severe vomiting and diarrhea for several days. After that he absolutely didn't want to use the potty again.
I decided that it was a battle I couldn't win, and that fighting him over this would be traumatic for us both. I put him back in pull-ups and let him be. It was a full year before he was potty trained. He come home one day from preschool and mentioned that no one else was in a diaper. He started using the potty every time he had to go from that day forward without me asking or prompting him.
For our family it worked to just leave him be until he was ready. I tuned out people who were judgmental about his age and remembered every kid is different. He is now 5 and delayed potty training has had no impact on his happiness and success in preschool. In retrospect I am glad that I didn't turn the potty into a confrontational issue that we battled multiple times a day for some period of time.
So, if your son isn't ready to try again consider giving him some more time in a pull-up. Remember that in the long run the age you started using the potty really won't affect the rest of your life at all! Hope this helps - S.