Been gaining n losing weight period is 4 instead of 5 stomach hurts if I don't eat some pains in right side could I be pregnant?

Get tested. If you have been sexually active, especially if you have not used birth control, you could be pregnant. The easiest way to tell is to get tested. The symptoms regarding your period are not clear to me (shorter period vs. Shorter interval between periods), but many of your symptoms could be related to other problems such as peptic ulcer or gall bladder disease.
Could be ibs. Check for pregnancy - could also be inflammatory bowel disease get evaluated.
Easy to check. Do a urinary preg test to make sure you are not pregnant. Assuming you are not it would be reasonable to check out your stomach and gall bladder as the cause to your symptoms.