Lower Left Quadrant Pain- Gastroenterology?

I'm 24 year old female who has been having lower left quadrant pain for the past few years. I've been experiencing bouts constipation (sometimes upwards of 5 to 7 days.) The constipation is then followed by weeks of diarrhea. The pain and the frequency of the bowel disturbances have increased. I have tried fiber supplements and other over the counter medications to try to relieve my symptoms. The pain is really getting to me and it is on my lower left side near my hip. It also hurts worse when pressure is applied near that area of the abdomen. Please let me know what you think this might be. I am going to make an appointment to see a Gastroenterologist this Monday.