Basically, the difficult part is knowing when to take a pregnancy test. Sometimes with PCOS the woman does not ovulate, in which case there is not only a long time between periods, but the cycles are also anovulatory (no ovulation) and therefore unable to result in pregnancy.
If you suspect you are pregnant, take a pregnancy test. Remember, however, that it can only give you a conclusive answer as to pregnancy resulting from sex about 2 weeks prior to the test. If you have had unprotected sex since then, you may need to repeat the test.
Good luck!
Rachel