Intense stomach pain after not going to toilet?

I never used to go to the toilet during the night, and always waited until the morning. However, now during the last few days I have noticed that if I don't go during the night, after I go during the morning I get intense abdominal pain and feel physically sick (like about to vomit). Afterwaters, I also went to the toilet again with diarrhea. My stomach feels really unsettled, until late afternoon (1pm). Why is this?, is this something that I should worry about?. Might I have IBS?.