I received 2 doses of pfizer vaccine in june 2021. they messed up my next 4 cycles and made me spot for 1 week before my period. i want to get a booster shot now, but am actively trying to conceive. should i get it? is it safe for me/future baby?

Yes, you should get it. By what I have known so far, the third dose of Pfizer may not protect you from Omicron infection but a pregnant lady and her fetus are much safer after the booster dose than her counterpart whose vaccination status is not up-to-date if both are infected.

MRNA vaccines are known to cause menstrual disruptions. That said, you should still get the vaccine. While you may have a few months of irregular menstrual cycles, in the long run you and your future baby will be more protected. Pregnant women are more likely to have serious complications from Covid infection. You should also take other precautions to avoid infection.