I have sharp pains and pressure in my rectum. sometimes i scream in pain. what causes this?

Lots of stuff: How long have you had the symptoms? Brand new? See your doc asap. Could be diverticulitis, appendicitis. More chronic? Could be spasm (proctalgia fugax-more common in uptight men), more common stuff includes anal fissures (tears), hemorrhoids, inflammatory bowel, also tumors, isolated rectal ulcer; less likely diverticulitis, or appendicitis. Could be gyn issues still need to see your doc.

Hemorrhoids?: Without an exam, it is hard to know what is happening. Hemorrhoids are very common and can present with pressure and pain. Other GI issues such as diverticulosis, celiac disease, ibs, ibds, imbalance in gut bacteria, etc can result in various symptoms such as constipation, diarrhea, gas, tenesmus (rectal spasm), etc that can contribute to your situation. Hemorrhoids are most likely. Water & fiber!