Period not here 😪

Alright so I got my period February 17th-22nd. I had protected sex on March 11th. There was a condom AND the withdrawal combined and i'm sure I was in the perfect use of both because he finished outside of me and the condom was fully intact. On march 12th I visited the Gyno and there she gave me a blood pregnancy test because I was worried then about pregnancy from having sex in January and she told me that was definitely enough time to get a very reliable negative and I could start my birth control.

Just some info about the combination of both form a site specifically for sex education. Well I never got my period in March. I took a test 3 weeks and 2 days after sex and two weeks after my expected period and this is what I got

Now I know pregnancy tests are 99% accurate and so I'm 99% sure I'm not pregnant. I followed the directions to the T and peed in a cup to absorb the pee cause I am a terrible Aimer and I also like to do multiple tests) Why else could I have missed my period? Should I still be worried I could be pregnant?

(Disclosure: I am irregular so I have never tracked my periods and was surprised by them. I do specifically remember one time in high school when I missed one month got it the next and then missed another month and got it the next.) I don't have any signs of pregnancy or period heading it's way. Boobs feel fine, I get nauseous but it's because I get anxiety real bad and it makes me feel sick. And I have stomach problems in general. I get slight cramps sometimes but I never know if they're in my uterus or I have to use the bathroom. Lower back hurts sometimes but I did injure my lower back a few years ago and it'll hurt from time to time. I have been getting more frequent on going headaches but it could be the pollen or because I have migraines(diagnosed by a neurologist). 🤷🏻‍♀️