urine stops midway and cannot be controlled

Hi. So about a week ago, I decided to go pee when I felt a little urge to do so. The the pee didn't come out at all no matter how I press and massage my lower abdomen. I tried to stimulate from the inside of my private parts by rubbing and pushing some sort of a sac inside, but when I felt the urge to pee, the pee came out very little, then it stops, and the sac became very hard like it's full with urine but couldn't come out. I tried pressing it, but not a trickle came out. The sac remained hard for a while before it relaxed. The urge to pee was still there for the whole day. I went to the mall and the urge was suddenly intense. However the urine came out just a little, so I got out and continued walking around the mall before 3 minutes later, I had to go again. After 4 much-too-frequent-and-too soon trips after, I contained myself in the mall's toilet for 5 hours! The urge is really torturing me. The next day when I finally got to pee, the urge was so sudden and intense and I have very little time to reach the bathroom. Often, I burst in my pants before I could reach there. I cannot control it at all! The most frustrating part is the urine flow stops midway, but the desperate urge to pee is still there for a few moment before it became just a mild urge or very rarely, none at all. Please help me. This problem makes it very hard to juggle my life as a student and a part-time worker. In fact, I just quitted my job and often skips classes because of this problem.

I am a 19 year old college student. I have been on birth control pills for almost 2 months and am sexually active with ONLY one partner. (We have sex 1-2 times per day, but stopped when this problem started) I never had any surgery, and I'm certain I'm not pregnant as I'm on my period now. I also don't drink or take drugs.

Thanks.