What Causes Nausea, Soreness In Abdomen And Low Appetite After Doing Sit Ups?

Alright, 19, male very physically active. I love being outside, I haven t drank much water but I ve sweat easily way more than I ve taken in. So this stomach pain started a few days ago, I did a lot of sit ups, and feel very sore from them. But.. My appetite is gone, my stomach is sensitive to palpation in all areas, especially lower right. Hurts to get out of bed, and especially to laugh. It feels like my stomach has that feeling you get when you laugh for a very long time, almost the same as a rollercoaster. I feel nausea most of the day. This has been going on for approximately 3 days, and doesn t seem to be getting much better or worse. To FURTHER COMPLICATE THIS, I m going through opiate withdrawal so pain and nausea are both amplified. What should I do? Medical student here btw.