Before This, I Have Irregular Periods Nostly Very Long Heavy

before this, i have irregular periods nostly very long heavy periods. so doctor gave me norethisterone. 5 mg 3 times per day for 3 weeks. problem is sometimes i forgot to take them on time and usually end up eating just one or 2 pills per day. will not taking it as prescribed and not on time affect anything? im trying to conceive. previously had intercourse. im confused whether to keep taking norethisterone until i finish it or stop taking it, in case i get pregnant. because i've read that we should stop taking norethisterone if pregnant.. but ive also read that after stopping taking this norethisterone, i will bleed and this will flush out everythg including any embryo.. i really want to conceive... we've been trying for 9 months and still no luck. husband and i are far from each other due to work commitments. we only get to see each other during holidays or weekends. please advice. thank you.