What Causes Missing Periods?

"I was raped the begining of april. the monday afterwards (3days) I got my period a week early. I had it for 4 days really heavy and it ended (which is almost normal cuz i usually only have em for 5 days) its been almost 5 weeks now and no period. (I usually am on 5 days then off 3 weeks and back on again.) Can I be preg?