Husband got someone pregnant and i still cant get pregnant

My husband and I have been trying to get pregnant for 6 months now he cheated and got someone else pregnant (she had a miscarriage) i stayed with him. But I’m wondering why i haven’t got pregnant yet we do it on all my fertile week. We even got the opk and check bbt. I’m not understanding. I went to the doctors and they said I was completely healthy. Now I’m 5dpo and don’t feel any different. I’m scared this is gonna tear our marriage apart