Pain In Side Of Rib On Doing Activity, Started After Exercising Without Warm Up. Treatment?

Hi, I am 20 years old male and I recently got this pain on my right side under my rib, specially when I twist and run.Sometimes when I rest or do not move it feels like its ok but when I move back or do some activity the pain is also coming back. I think its some air stuck in there but when I jump it feels alot like something is in there and moves,I hope its not my liver . And about why its happening, I can say I started an exercise without any warm up maybe. I ve had this pain since 3 days ago, and before that I never had any serious disease or etc. I do sports like Football and Fitness but irregularly.My diet is fine I think and I am in good shape as well. I was wondering if anyone can tell me,what my problem is and how to treat it. thanks in advance though.