There are many types of cysts you can get on your ovaries, but if you have PCOS (Poly cystic ovarian syndrome) your chances of getting pregnant are slimmer. When a woman ovulates, they do so because of a release of hormones - PCOS is a condition where those hormones are out of balance. Often if a woman has PCOS they simply will not ovulate. This is what causes the irregular and missed periods. The cysts themselves usually last a few weeks, then go away. This would also be the reason why a doctor could not find cysts on an ultrasound if they had found them before.
If you cannot see a doctor, do your best to keep a healthy weight and lower your sugar intake (PCOS is thought to be linked to insulin levels and type II diabetes.)
If you can see a doctor (remember there are many low cost clinics that go on a sliding scale based upon your income) they will probably start you on a drug called Glucophage, or Metformin - it's a drug for diabetics that also helps women with PCOS. If that doesn't work, the next phase is to try Clomid, a fertility medication, then both of those in conjunction.
Hope this helps, and good luck!