I'm 46. My period which is normally regular is 2 weeks late. I had had unprotected sex 3.5 weeks ago. I have taken 3 pregnancy tests with negative on all 3. If I go to my Dr. Can they do a blood test to see if I'm pregnant or if I'm going through menopaus

Blood test will help. By doing blood test it's possible to differentiate between pregnancy, delayed period or menopausal changes. Though fertility generally declines with age, keep in mind that most unplanned pregnancies happen before 20 and after 40. Use of birth control is always a good idea.
You Are not pregnan. Most probably an irregular period which are not unusual years presiding menopause due to unovulatoty cycles which are common at this stage of life.

Related Questions

Period 2 days late, had unprotected sex, two negative pregnancy tests. Will a blood test be accurate around this time?

Yes. A irone test should also be accurate,bit a blood test would certainly be an appropriate next step,prior to doing any further testing or giving anyeds. Read more...