You could be unlucky in that bedbugs are very specific about who they bite. They're not species-specific, ie they will happily munch on cats, birds, rodents etc as well as us, but once they find a good meal they tend to go back to the same restaurant. I am reliably informed that in a bedbug infestation, some of them will eat you and only you, and the others will eat the other guy and not you.
You're positive they're bedbugs? They're on the increase, but 3 different occasions sounds like a lot. As Rabelais says, not everyone will react - but there must have been a lot there to even get to you once. Most people never come across bedbugs - if they've been positively identified then it's an environmental health issue and must be dealt with.