How early can you take a pregnancy test? Help plz!!?

Okay, so i have missed my period it has been about six weeks, but my period is irregular. I have had unprotected , but my boyfriend pulled out, i know that you can still become pregnant that way. I have taken a pregancy test before and it was negative, but that was before i really missed my period. The last time i had wasn't very long bc someone walked in and he pulled out and never came in me and didnt *** when he pulled out. So could i still be pregnant.. I feel like i am experiencing some symptoms, but idk if i'm just scaring myself.. besides my missed period i pee very frequently, i have back pains, i'm very tired but can never sleep bec my back pains are so intense. i do have morning sickness, but i experience it more at night then i do in the morning. So is there a chance i can be pregnant, and if there is how big of a chance?