I'm 45, I didn't get my period this month. My husband had a vasectomy 4 years ago. Is it too early to be going through menopause?

No. It is not too early to be "peri-menopausal" or around menopause. Unfortunately pregnancy is not impossible if your husband never got his vasectomy checked to verify "no sperm". Any chance of pregnancy and you should do check - if not then you may just have erratic periods or you may be experiencing menopause. Only time will tell.