While I'm sure there could be physiological reasons, sometimes its just a matter of getting to know your own body and also unblocking the negative thoughts of inability by just going with the flow. Depending on your upbringing climaxing could be blocked by feelings of guilt or shame. There is nothing shameful or guilty about self-exploration or even a close intimate relationship with a partner. Take it easy and forget about the destination and just enjoy the journey.
If there is no psychological component, then I would see an gyno/OB to determine if you might be having some type of physiological condition.