No you cannot get pregnant the day before your cycle starts. Your hormone levels wouldn't be right. I think it's 2 weeks before your cycle starts that you might be able to conceive no matter what the length of your cycles.

Hi, you will need to either find a way of identifying when ovulation takes place which should be around 14 days to your next period which in your case is extremely difficult or see a doctor. I used to have very irregular periods and never took it seriously. Last week I went to see a doctor after trying to get a baby for some time and was found to be having Polycystic Ovaries. I have been out on treatment to help regularise my cycle and force ovulation on a particular day. In a way my advice is do see a Gyna or GP.

I suggest charting your basal temp. I've had irregular periods for my entire pubescent life and when my husband and I started trying to have a baby my doctors all agreed that charting your basal temp is a good indicator for ovulation. There are many free online charts and the only thing you'll need is a digital thermometer.(although a mercury thermometer will work but the movement for getting the mercury down might mess up your results, also a digital thermometer can be read out to a tenth of a degree for more accurate readings.) It takes a while to get the hang of taking and reading the temp correctly and if your not on any medicines for regulating your cycle it might be a long time before you notice the trend and are able to take advantage of it. Good luck.

i have polycistic ovaries too. it's difficult to know when you ovulate so the best thing to do is to just have sex everyday - that way you have it covered for when you do ovulate. well, that's what i did and i can't believe that i got pregnant quite soon afterwards. i also had irregular periods, had no idea if i even ovulatede and thought i would never be able to get pregnant and all it took for us was just sex every day consistently and all of a sudden it happened!