I take evening primrose oil with Vitex and never had a problem, and I know a lot of women take them together. But if you're taking Omega 3-6-9 the EPO would probably be an overkill. EPO is rich in Omega 6, which is what helps your body. You can also try adding a balanced B vitamin complex. For example, I take a B-50 complex. It should be OK on top of the prenatal vitamins, just be sure you keep vitamin B6 consumption below 200 mg a day; it is dangerous in high doses. Beware that the B vitamins will probably turn your urine bright yellow; this is a normal side effect since most (though not all) excess B vitamins are execreted in the urine. Some women have noticed B vitamins helping with their O and length of the luteal phase.
If your lack of period goes on too long (usually it's 90 days or more of no period), you can see a doc and they can help jumpstart a period by giving you Provera or Prometrium (hormones again, unfortunately).
Other things that are said to help increase fertile cervical fluid are drinking plenty of water daily, cutting down caffeine, drinking 1-2 cups of green tea daily (but not more than that because it can interfere with absorbance of folic acid), and eating baby carrots (something about the beta carotene they contain I believe).