Heya astro, let's try something here.
Lets examine the evidence. You have 3 presumable bite marks on your stomach which occurred during sleep. Do you sleep without covers? Do you sleep outside? Do you sleep in a cave?
I assume you sleep with covers and it's a no for the other two. Moving down that path let's assume that a bat lives in your bed room or house. Firstly bats LOVE dark places. I assume you have already looked at those locations like under your bed, dresser, night stands, etc.
Bats by nature are easily threatened meaning while looking for them you would have spooked it in your room for instance. I assume that is not the case. That would mean the bat would have hidden in your house until lights went off. Then it had to find you.
While all that is reasonable, let's further assume it did find you. Now it would have to land on your bed, then crawl under your covers onto your stomach and finally bite you. Then crawl away from your covers, and finally return to it's hiding place. Now here is the kicker to this. Why would a bat choose your stomach under covers rather than an exposed location like your face or scalp or arm?
I do understand your fear and anxiety associated with bats, however the likely hood a bat would bite you is extremely rare. Not to mention the most common bat you will see is a fruit bat and not a vampire bat. Further more vampire bats feed on animals over humans due to location and accessibility. Your fears are warranted, however your bite marks are more likely spider bites and/or bed bug bites. Non lethal and non threatening unless you live outside in the amazon.
Best advice i can give you is to research bats more thoroughly. Face your fear and learn their patterns and diet. Humans are not their top meal choice :)