Your doctor will likely prescribe progesterone cream to lengthen the phase between ovulation and the onset of menstruation. If this phase is too short, conception may occur and be miscarried. Progesterone aids conception, in this way, primarily by lengthening (what NFP users call) “phase three.” You may also try to use B6. My wife had a short phase, like this (which would also make her prone to miscarriages), and has had it corrected by a regimen of over the counter progesterone cream and 100mg B6 vitamin taken three times daily (it is water soluble, which means you must spread out the dosages throughout the day). Talk to your doctor about trying these things, because they have completely fixed my wife’s problems.
Also, the admins are probably going to point out that nutritional advice is against the rules - so make sure to talk to your doctor! :o