Is human chorionic gonadotropin test a reliable indicator of pregnancy?

Hello doctor,

I am a 21-year-old female. It is been approximately 20 weeks since my last sexual encounter. There was no vaginal-penile penetration; it was done through dry sex or outercourse (each person had 2 layers on), but some ejaculate leaked through the condom. Since then, I have had four periods after missing it in February. After the sexual encounter, I got my period, and later an HPT (home pregnancy test) test was negative. I then got my second period, and again, an HPT test was negative, followed by a negative qualitative serum HCG (human chorionic gonadotropin) test. Since then, I have had my third and fourth periods.

Based on the negative pregnancy tests and regular periods, can I safely say that I am not pregnant? I am getting concerned because I have been gaining weight lately, and my stomach has been getting bigger. A few days ago, I experienced some weird lower left abdominal pains, but they have gone away now. Can I conclude that I am not pregnant and there is no need for retesting? I got worried because some women said they experience monthly bleeding despite being pregnant.

Thank you doctor for the reply,

Is a qualitative serum HCG test still trustworthy? I did not have a beta HCG test. Also, is it possible to still have monthly bleeding despite being pregnant?

Thank you doctor for the reply,

I do not have a physical copy of the report as I disposed of it, but the result was printed as "NEGATIVE." They used Immunochromatography Assay.

Thank you doctor for the reply,

So, in summary, I am not pregnant?

Thank you doctor for the reply,

Take care as well!