How Can severe Abdominal Pain Along With Gastritis be Treated?

Thank you very much! I m trying to figure out if I have a stomach virus & how long it might last. I had abdominal pain and a lot of gas and burping when I played tennis on Sunday afternoon. So, I had to stop my tennis game. I was able to have a normal bowel movement & stopping my activity ended the pain, after a while. I thought it might me due to the veggie burger that I ate about an hour before I played tennis. Later, I realized it might have been the tomato slice I had on the veggie burger, since the tomato was very ripe & soft in places. But, I have had no vomiting or diarrhea...just an upset stomach and headache, fatigue. My head doesn t feel hot enough to have a temperature. I have been eating only toast, rice, crackers, and baked potato w/ a little butter or margarine since Sunday. The headache started on Monday and was mild until Tuesday. Yesterday afternoon, I took a Tylenol. I noted that the expiration date had passed, but hoped it might still be effective. It wasn t. The headache is back, today. I ve just had some apple and Cheerios with Almond milk for breakfast, today, & yesterday...plain oatmeal with a few frozen blueberries on Tues. for breakfast. Moving / walking around makes my stomach achy, but not sharp pain. Is this a virus? A friend thinks I should go see my doctor, but I thought w/o a fever, he could not really do anything. I thought it might be a touch of a bacteria from the tomato. What do you think & suggest? Wondering how long this might last and should I go see my doctor or not? YYYY@YYYY