I Expected My Period On June 5 & It Never

I expected my period on June 5 & it never came. Now 16 days late & 4 NEGATIVE home pregnancy tests later (Clearblue brand), I'm left feeling so worried. I took 2 HPTs 12 days after my expected period date- negative. Then I took 2 HPTs 14 days after expected period date using first morning urine- negative. Could these HPT results be wrong or inaccurate?

My periods are usually on time every month. I have never missed my period before. I am sexually active & do not use birth control- only condoms.

I want to note that I have also had very minor lower back pain since May 31. I took 1 Tramadol pill to ease the back pain on June 7. Could that have made me miss or delay my period? I have also felt bloated, constipated, & sometimes have tender nipples. Other than this, no sickness, nausea or headaches. These feel more like PMS symptoms.

Please, I need some help. I am so confused & scared at the possibility of being pregnant! I am 23 & am not ready to be a mother. I just want to know if this situation is relatable to other women's experiences.

What next steps should I take? Thank you.