Just diagnosed w/thrombocytopenia MPV 10.1fL. I'm on Propranolol & Topamax (topiramate) for migraine. Which is likely cause? If I stop meds will platelets return?

You must discuss it. Be certain that your Dr(s) know about the drugs you take and urge them to work on the best resolution of this situation. It's way to delicate, complicated and important for you to manage on your own. Their training is for this sort of thing and it's their responsibility to handle it. Be helpful and firm and persistent but trust experts on this.