Kegbuster, there are rather a lot of errors in your post.
1) No - under no circumstances whatsoever should you keep carb heat on, and particularly not if you might need to go around. Apply it, rid yourself of ice, then cancel it again.
2) You cannot tell from the MP gauge if you have carb icing. Indications are ambiguous. Operate the aircraft in accordance with the POH. Further, there are a lot of light aircraft out there that do not have MP gauges at all.
3) No, applying carb heat CANNOT cause carb icing.