birth control!!

so i take my pill at 9pm every day, but sometimes it makes me nauseous and i throw up a couple hours after taking it, do you think i should be concerned that it is not as effective as it should be since it makes me sick sometimes (not every night, maybe 4-7 times a month) this is the third kind of pill i’ve been on yet it still makes me nauseous and throw up sometimes... does this affect the effectiveness? should i be concerned about getting pregnant because of this? any advice?