Urinary problems of all sorts are common with MS
Retention is a serious issue, as urine can back up into the kidneys and
cause all kinds of problems from there. Also, the longer urine is in the bladder, the greater the chance of infection. UTIs can be dangerous, as many here know from experience.
I urge you to see a urologist, or if possible a urogynecologist, as soon as you can. There are tests that can tell a lot about the state of your urinary functioning.