Hi, I'm 18 years old and I have had sex with my boyfriend in July ( however I don't know the exact date). We used condoms as a form of birth control and there was no ejaculation, he wore the condom before we had sex so no precum could have come in contact with my vagina. My periods are very irregular and I do not keep track of them , however I never missed a period. I am not sure if my period came after we had sex however I know that I missed my period in August. I took a pregnancy test and it came negative. Can I be pregnant ?

Well if you have irregular periods then its hard to tell check with your doctor take a blood test and how have you been feeling as in any changes in your body that might make you think your pregnant?

In August when I was supposed to have my period I saw small amount of spotting but it only lasted one day and it was not very heavy, however I do not feel any other changes in my body, I don't know if it can be implantation bleeding or not because it happened more then a month after we had sex, Do you think there is still a chance I might be pregnant since we used condoms and no ejaculation was present?

Nobody will give you an answer to that on internet. It could be a yes, it could be a no. The only way you'll know is by visiting a doctor or getting your period.