I'm confused. Do you want to be pg or not? You're freaking out because your period hasn't started and you don't know why. But you won't take a HPT. Do yourself a favor and take the test. If it's negative stop stressing because it WILL delay your period. You don't have to physically feel stress for you to be stressed. All these anxieties and thoughts you are having can cause stress and delay your period. Plus, you're only 20. Don't rush things. You have plenty of time to become a mom. Live life first. Are you married? If not, I suggest waiting. A child deserves a mom and a dad. If it happens you get pg that's one thing but to actually plan on becoming pg without a stable spouse is not fair to a child.
if you had unprotected sex u could be pregnant or have an STI or STD
if its your lower back thats hurting it would be consistant with either
if youve not had sex then you could have a cyst