Ok So My Doctor Had Prescribed Me Phentermine 15's I

Ok so my doctor had prescribed me phentermine 15's I don't like to be pushy but it's not curbing my appetite so one day I took two and it did the job... Always trying to research this I keep seeing dosage 37.5 which is what my friend told me to original ask for I don't want to feel awkward by asking so how would I do so?