How many BMs per day are you having?
How much pepto bismol are you taking? One of the first-line treatments for microscopic colitis is in fact pepto bismol, at up to 8 doses a day (best if you can spread it out over the day), for a couple of months if needed.
If pepto-bismol can't control it, your doctor can prescribe entocort or uceris, two formulations of the steroid budesonide. That usually works well and quickly. But it's best to only take these for a few weeks at a time (steroids over a long period of time can have bad side effects).
Sometimes people with micro-colitis go on one of the mesalamine drugs like Pentasa or Apriso or Asacol or many other brands and generics. You can take these long term if needed.
For the time being, use more pepto if appropriate, and make sure you're getting enough fluids - water, soups, watered-down gatorade, things like Boost or Ensure.
Signs of you being too dehydrated and needing an IV of fluids at urgent care include dry mouth, dry eyes, lack of urination and/or dark urine, feeling weak or faint, skin that "tents" when you pull on it (ie, pull on the skin on the back of your hand and it should return right back to normal. If it stays up like a tent for a second or two too long, that's called "tenting" and can be a sign of dehydration.)