Can A Missed Period And Symptoms Like Nausea, Sore Nipples Indicate Pregnancy?

last month i got my period exactly 1 week late and it was just like a normal period. but this month, 28 days later from my last period i havent got one. ive taken 3 pregnancy tests at 3 different times .and they were all negative. i just took one 28 days from my last period but still negative. i feel nauseus and i can see veins in my breats but they are not tender. my nipples have been very sore tho. i dont have any other symptoms. could i be pregnant? i dont know what to do... im only 16 and im very scared.. i thought i was last month, but since i got my period i didnt think anything of it, and i was very stressed out at the time and so i thought maybe i might have lost it or something.. PLEASE HELP !