Pain in lower left side of belly.

Pain in lower left side of belly and I feel some swelling on pressing there. Seems like a muscle or a nerve or large intestine Its something elongated rod like but swollen in the middle. It pains more when tummy is gassed up. When i am lying on my back i can easily feel the swollen area but only on pressing there and it pains on pressing only. I have a bad habbit of waking till around 3am in the morning and since a week or so i am actively playing football at around 10pm after having food. I think I have this occasional pain in left side since about 2 years but as it never became any serious so i never consulted a doctor. I always thought it could be gas but now I am worried if its kidney stones, colon or prostate cancer, ulcer or what not. I have pain in lower back area since 2 days but that i think is because of football not sure. Kindly provide some advice thanks.