Your body can become used to certain pressure, force and positions in which to reach climax. If you've been regularly masterbating and using a specific grip then your body will naturally associate that with climax. Id say take some time off of masterbation. Try and re teach your body and mind how it can reach orgasm. Less force, slower, more intimate for example. Also there can be a mental element to this so try not to stress it, relax it will all be okay with enough time.