Best advice is to see a Dr ASAP. Your cycle is not normal and you need to be seen for it.
Yeah, I agree with Vance, you should see a doctor about your irregular periods. It's not that unusual, and there can be a number of causes (e.g. many top level female atheletes have infrequent periods, apparently). It would be good to know why, and what should be done about it, if anything.
If you had sex shortly before your period, and you have had a normal period since, I think it is unlikely that you pregnant.
Whether you are even capable of getting pregnant, with your irregular periods, only a doctor can advise you.