I had.sex three days after my period and now im crampn so i wanted to no can i b pregnant i have a 4 .month old bby?

Likely no: If you're saying you had sex 3 days after your period started, it's highly unlikely (though not impossible) that you got pregnant. If it happens in future, remember you can always take plan b. Or get a more permanent method of birth control if you don't want to be pregnant. Practice safe sex rest of month and if you miss period, take a test. But highly likely no.