Penis length and vaginal depth both follow normal distributions with (aroused) averages around 5 inches; (makes sense that the average penis fits perfectly in the average vagina.) If your boyfriend's penis really is 7.5 inches that puts him at more than 3 standard deviations above the average length of a penis and more than 2 standard deviations above the average for vaginal depth (in short, his penis is longer than 99.7% of all penises and 95% of all vaginas.) So, to your question, chances are good there is nothing physiologically wrong with you and your boyfriend just needs to be more careful (attentive to you) to keep him from injuring you; try positions that give you more control. A bruised cervix can be extremely painful (to the point of debilitation) and can take quite a long time to heal, so take extra care.
Trying different poses may help you to accommodate his length. You may also consult your gynecologist to rule out any structural problem in your vagina.