What Does Frequent Lower Rib Pain Suggest?

After training at Olympic style Table Tennis (TT) for two to three hours, I frequently experience pain just under my left side lowest rib area. It comes on always on the drive home, approximately 15 to 20 minutes after the training session. I use my left hand in this sport, with probably at least 100 large fast looping strokes starting near knee level and finishing near a military salute position. The torso is twisting on all of the fore mentioned strokes. I can dramatically lesson and sometime stop the pain by applying constant pressure with my fingers by pushing in on the area approximately 1.5 to 2 of penetration. It always goes away in 10 to 15 minutes from when it started(still while driving(seated position)). I usually eat a Honey Crisp apple while training and drink approximately 25 ounces of water throughout. Mentally, I am usually stressed on not preforming better (loosing certain matches that I should have won). I train TT approximately 3 to 4 times a week. I do not experience this pain from any of the other sports I do, except I always get it when I jog approximately 2 times around a track. Again it goes away even if I keep jogging further.