Greenish, algae colored feces, gas cramps

Hi, over the past year I have been having some pain in my lower abdominal area at random times due to extreme pressure when trying to relieve myself. The feces during the time periods are usually diarrhea and the movements are extremely painful but are relieved once I actually go and the gas is released as well. The doctor just told me to wait to see what happens but because the painful movements are so inconsistent I cannot really give many consisten examples of the problem. Recently the problem has gotten worse again and has happened 5 or 6 times over the past week and now the feces is a greenish algae like color. I have not had any real changes in diet and am wondering what could be causing this and if it is something I really need to have checked out. Thanks

[Rylecx22]

also I am only 18 years old and have no other health problems