My boyfriend ejaculated in me yesterday and the day before is it possible I'm pregnant?
And how many days should I wait to go check if I am pregnant or not?

If you didn't use any protection then I'm afraid it's a case of wait and see. Use protection next time.

Anytime you have sex, protected or not, there is a risk of getting pregnant. Not using any protection just greatly increases those chances. You very likely could be pregnant... or not. Only time will tell. Wait for your next period. If you miss it, wait a week, then take a test.