2 weeks ago, my urinary stream became weak & my bladder wouldn't empty completely. i also felt a pressure in my pelvic area while urinating. now, my urinary stream is normal but i still don't empty my bladder. what could it be? likelihood of tumor?

Not likely: Several different ideas come to mind, could have been a low level cystitis from activities, usually sexual, maybe due to ovulation or not drinking enough fluids. This may account for the pressure in the pelvis. Unfortunately, you need to see a health care provider and be examined and/or maybe tested with a urinalyses and possibly an ultrasound of the bladder . Get checked out!