Hello sir...Insufficient lubrication is also commonly caused by a drop in estrogen levels after menopause, after childbirth or during breast-feeding....Certain medications are known to inhibit desire or arousal, which can decrease lubrication and make sex painful. These include antidepressants, high blood pressure medications, sedatives, antihistamines and certain birth control pills....it can be psychological as well...for physical causes you need to consult physician or endocrinologist for detailed examination and evaluation with relevant investigations... If its psychological Consult nearest psychiatrist they will do the needful.