HELP!! Dog Problems !!!?

Sounds like she may have a "hot spot" or an itchy spot on the top of the base of her tail and she can't reach it. Call your vet and get their professional advice.

Are you walking, exercising her--providing her stimulating play? You didn't mention her age/breed. Tail chasing can be boredom. Where is she licking? The anal area, paws? There's so many questions to ask, answers would provide clues. What have you been feeding her over the past few days? Given her any new supplements/foods? Is she of good weight/overweight? Any changes in the household, new baby, new person move in--did she experience a trauma (dog fight?). You say she might be constipated? When did she last go? How often does she normally go? If she goes, are her stools normal, different in color/size?

I'd first assess her by observing her on a walk. If she's obviously in distress and won't walk, then, don't, but, that could indicate a problem. Dogs should poo at least twice daily. If you suspect a food problem, watch her poo and water intake. If she refuses food temporarily, that's OK, but, if she refuses water, too, that's not good. Dogs are sensitive to their environments. Changes may result in new behaviors. If traumatized, the behavior could be a reaction to that.