No, if you had not had af in 3 mths I would suggest telling your doctor as this is a sign of PCOS and means your not ovulating
A blood test is more reliable than a home pregnancy test,they are 98-99% accurate,and can be done as little as 7dpo.I personally would say not your not pregnant,however if you feel you would be 3 months by now.ask for a scan,this would show.they could be other underlying reasons why your not getting your periods.good luck.
It is quite possible... I had the same thing happen with my first son.. Even with a blood Beta HCG test it was negative. I was almost 5 months pregnant with him before it showed positvie.