How to tell if you've been bitten by a flea or bedbug?

My sister woke up the other day with 22 itchy bug bites all over her abdomen and thighs. We searched her bed to see if we could find any fleas or anything and we did catch a flea, but I doubt it could have bitten her 22 times! We recently went camping and I was wondering if maybe she picked up bedbugs? She was laying on her back, and there are no bites on her back. We don't have any pets and no one else has been bitten except her room mate who was bitten twice on the ankle and aside from that one flea we found, our house appears vertually bug free. How can you tell the difference between a bedbug bite verses a flea bite?