I Am 23 Years Old And I Missed Two Periods.

I am 23 years old and I missed two periods. The last one was on the 8th of June. I took about 10 pregnancy tests, all came back negative. In 2019 my gyno told me that I have PCOS, but then another doctor told me that I didn’t but that I am predisposed to cysts. I am really stressed because I have experienced lower back pain on the left side and I pee more frequently without drinking more fluids. Also, I have noticed lately that I don’t have so much discharge, but it is yellowish. What can the delay be caused by? Can all those tests be wrong?