Concerned

So, I’ve posted about this previously but I’m going on day 9 with no sign of my period. The last time i had sex which was 7 consecutive days on and off protected was end of December/beginning of January. I’ve had a period both in January and February, normal heavy flow two days (2 tampons and a pad worth heavy) and medium to light flow. They varied within -/+2 days of when predicted, so pretty much regular. I’ve had cramping and backaches as if it was coming but nothing. I know pregnancy isn’t likely but that .01% chance convinced me to test, BFN. At this point, i would be almost 2-3 months along. And without a doubt, it’s negative but i was gonna test just because google makes it seem like anything is possible when it comes to pregnancy. I’m 20 about to be 21, I’m not concerned about if i were pregnant. I’m just confused. I’ve had my period since i was 14 and I’ve never really missed a month... i don’t feel I’ve been stressed but maybe my subconscious has been stressed lol. I haven’t changed my eating habits and i haven’t gained a ton of weight or lost it. I’m 5’4 and 113 lbs. I’m tiny, so I’d notice weight gain. I have an appointment April 5 to get on birth control so I’m assuming this will be best to bring up to the doctor but i was wondering has ANYONE experienced anything like this personally?