Lightheadedness and Diarrhea?

I was diagnosed with mono about a month ago and i have no idea when i got it. In the last 2 weeks i've been having bms non-stop throughout the day. I have a fast metabolism so i go often already but now it seems ridiculous and yesterday and today i've had weird feelings of lightheadedness and its making me feel queasy. Anyway, should i take another trip to the doctor or am i dehydrated from the diarrhea? and also what could be causing my diarrhea (btw its not really that bad even, its just really soft)