8 days after period i have pink spotting, cramps and back aches. husband is fixed. never have spotted before. what could it be?

Occasional : Spotting can occur as a variation in many women's menstrual cycle. There are also several alternate explanations, but would wait and see if it improves. If not, see an ob/gyn doctor and get examined. Your husband being 'fixed' is not necessarily a guarantee that it worked 100%.

Variety of things: Women can have spotting at various times during their cycle and can be for a variety of reasons. Vasectomy is a very effective form of birth control but pregnancies can occur. (often if the man never came back for his follow-up semen analysis after the vasectomy. See your health care provider.