I have been having pains on my achilles, particularly if i maintain a certain position for about 45mins. when i stand up i feel the pain. ?

If the pain: is only in the Achilles tendon, you can try a shoe with slight heel elevation to prevent over-stretching. If pain extends into calf, it can be DVT and you need to see a doctor at once.

Either way, not good: I am not quite sure if you mean to say that your pain appears when you stand up, after maintaining your Achilles tendon in a certain position. as opposed to your tendon's pain begins after maintaining a certain position and hurts even more when you stand. Either way, your symptoms could signal the onset of a tendonitis that should be evaluated before the condition, potentially, get worse.