looking for advice on pregnancy/fertility

okay my husband and i have been trying to convince for the last year and haven’t had any luck yet. i don’t understand why, i have two kids of my own from a previous marriage. i did have the mirena for three years and i’m beginning to think it may have caused some problems. i just bought a fertility supplement to help boost things, but i also see people track things like crazy to see when the best time is etc. any recommendations on what i should be tracking or how to do so? or even some advice? i’m starting to feel hopeless and so is he. i just want to be able to give him a biological child, although he considers mine his own..