My bladder feels full even after going to the bathroom.?

Bladder fullness. This may be associated to infection with or without obstruction to the urinary flow. Check your urine for infection, treat with antibiotics. Might need tests like ultrasound of bladder before and after urination. Bladder spasms? Check. Urologist.
Lots of causes. There are many possibilities including cystitis, interstitial cystitis, or something pushing on the bladder such as a uterine fibroid. You may not be emptying, so a post-void residual should be determined--this can be from prostate enlargement, urethral stricture, a dropped bladder or neurological conditions that affect the bladder such as diabetes, ms, parkinson's, etc.