Missed period, negative test, pls help

Hi! I just recently started getting sexually involved with a guy for the first time and to be clear, we did not have sex. However, in the last time we did anything (the last week of May), he fingered me and touched himself. The reason I am stressed is because I do not correctly remember the order of events and I am worried he might have gotten precum inside me (he had not yet came, I do remember that). For info, my period ended about 2/3 days beforehand. I was terrified the morning after, so I took Plan B with the help of my friends ( I am 18). About a week later I got a light period that lasted a few days, which was about 3 weeks early and I know this is because of the Plan B. Immediately, I was relieved and thought I was in the clear. Now it is early July and I have yet to receive my next period and I am very stressed. A few days ago I took a test to ease my fears and it was negative. Still nothing !!! My friends all assure me that I am fine but my period just won't come. Could this just be stress or because of the Plan B? I do not know what to do. I read that taking high dosages of Vitamin C can induce a period. Should I try? Thank you in advance for advice. For reference, my period is almost always irregular and I have skipped months before, lately it has been pretty regular however.