When is it TRULY safe to trust a HPT result if you do not get periods?

[LylaKat]

Hello all! I am new here, but am having trouble finding an accurate answer to my question. I do not get periods, and have not since February of 2016. The doctors believe it is because I am underweight, but I think I may actually have undiagnosed PCOS. Regardless, I do not partake in sex very often, but did on 4/14/17. That is the only time this year that I have. I am not on any type of birth control, but we do use condoms. We had sex a few times that day, and because I am paranoid, I did not let him ejaculate in me- even with the condom on, and he urinated after each time we were intimate. The last time, we did not use a condom right away (this is where my cause of concern comes from) though he did not ejaculate or even get close.
One week later, I noticed some light pink/brown spotting. There were small particulates that did not look like clots, but more like a small string of tissue (white in color) with a black tip at one end. This happened on two occasions when I urinated, and the spotting lasted on and off for about a week, where I would see faint color on toilet tissue. This could have either been a small period, implantation bleeding, or perhaps a sign of ovulation. I am not sure though. I have felt fatigued almost every day since intercourse. It has been almost 4 weeks now, and I am experiencing occasional sensitive and sore nipples, nausea, cramps, and loose stools. I have been very worried that I may be pregnant, so these symptoms may also be occurring from nerves. I have taken 4 pregnancy tests, all First Response, and each one has been a very clear negative. My most recent test was yesterday, at 24 days since intercourse. Is it safe to say I am probably not pregnant, or am I just testing too early?

[RockRose]

It's pretty safe to say you're not pregnant.  The test should be accurate about 14 days after unprotected sex.