I am in need of some serious advice, could I be pregnant?

Ok...so I am always like clockwork, every twenty eight days I will have a period! I will start between the 25th and the 28th of the month, and so far I still have not had a period. I have taken a HPT and a blood test with the doctor and both are negative. However, on the 23rd of February was when I took out my last NuvaRing and I did have a menses, very light, but I did have one. I am now late on my period and want to know weather this is in correlation to the hormone levels, or if I might have tested too early! I really need some advice and some answers because I am getting kinda nervous! Plus, I really would love to have another baby :D