Lower Abdominal Pain/Digestive problem?

Hi

I am a 28 year old male.   I cannot remember the last time I went to a doctor besides a sprained wrist and i am generally healthy, so i am just a little hesitant to run to the doctor over something that might be nothing to worry about.

Over the past 2 months i have had two 'episodes' of GI problems, they last a few days or up to a week and then subside.  

Symptoms include:

-overall feeling of fullness, especially in lower abdomen just above pelvic bone.
-frequency in urination
-frequency in defacation (feel like I have to go more often)
-overall, pretty gassy and sometimes when i feel gas passing down colon or rectum, there is a mild pain that lasts a second
-when i sit down or stand up there is a dull ache in my rectum area that lasts literally one second.

Has anybody dealt with this?

Retrospectively, if i think about it, it usually happens after a few days of unhealthy eating (greasy foods, pizza, meat)  

I do drink alcohol regularly as well.   Not sure if that contributes

Thanks for your help