It's not normal, no... but if you have PCO, as you were told, your periods will be irregular, both in lengths of time between periods and the flow. I can't speak for definite, as I am seeing my gynae for the first time next week, although I was dx'd in March., but I get exactly the same. My periods can just be a day's very light, or weeks of heavy or anything in between; with time between being a couple of weeks to nearly a year. My GP doesn't seem too concerned about it on a day-to-day thing, and just said that we'd address it when I think about having children. Don't fret too much about it, but if you're really worried, speak to your GP. Also, keep a log of when you're on, off and how heavy... itll help.
Good luck
Hello,
This irregularity in periods is due to PCOS. The menstrual irregularities of PCOS are accompanied by a lack of ovulation, so affected women may experience infertility. An increase in the production of androgens (male hormones) by the ovaries in PCOS may result in excess hair growth in areas suggesting a male pattern, known as hirsutism. Oral contraceptive pills (OCPs, birth control pills) are used in some women with PCOS to establish a regular menstrual cycle and to reduce the risk of endometrial hyperplasia and cancer by establishing regular menstrual periods.
I hope it helps. Take care and regards.