I haven't had my period for 2 months. i've been on birth control for many years. i know for sure i'm not pregnant. is this normal?

Yes it happens: By pills do thin out the lining of the uterus, the so called endometrium, it can become so thin over a longer usage , that it is even too thin to bleed altogether , while you are at the end of your pill package. This effect is even more common and does happen faster with the newer very low dose pills with the fewer hormone free pills. So what you are experiencing is very likely normal.