Hi there, Thanks for your query. If increased thirst is the cause of taking lot of water, it may be suggestive of either, dehydration; or, uncontrolled blood sugar. Redness and sensitive foreskin is apparently due to a local infection, which too favors uncontrolled diabetes. Metformin is known to cause diarrhoea. It would therefore be advised to switch over to another anti-diabetic drug, the dose of which should be adjusted so as to reduce sugar level to within desirable range. For possible foreskin infection, consult a dermatologist who will examine you and prescribe appropriate treatment. If you find my response helpful and informative, do not forget an “excellent” (5-star rating) to my answer, to ENCOURAGE ALL doctors- engaged in social service- to render sound advice to the FREE queries. Take care Dr. Rakesh Karanwal