You should consult with your Health Care Provider about the Medications you are taking and their effect on fertility. Some medications while taken alone may not be a problem but when taken in combination with other substance may pose serious risks. There is no substitute for a consulatation with a Medical Professional.
A few General precautionary notes, however these lists are not all inclusive.
Anabolic Steroids (used by weight lifters and other athletes) are known to severely impair sperm production.
Among other drugs that can cause male fertility problems are Calcium Channel Blockers (ie. Amlodipine, Bepridil, Diltiazem, Felodipine, Hudsonipine, Isradipine, Nicardipine, Nimodipine. Verapamil) Thioridazine (Mellaril, Rideril), cimetidine (Tagamet, Acid-Eze, Dyspamet, Galenamet, Zita), sulfasalazine (Azulfidine, Sulazine, Salazopyrin), methadone, colchicine, azathioprine (Imuran, Immunoprin), methotrexate (Folex, Matrex, Rheumatrex, Trexall), phenytoin (Dilantin, Phenytek, Epanutin), corticosteroids (ie. Hydrocortizone, Dexamethasone, Budesonide, Betamethasone, Prednisolone, Methylprednisolone, Prednisone, Triamcinolone), spinronolactone (Aldactone, Laractone, Spiretic, Spirospare)
Some natural substances like Saw Palmeto may decrease sperm counts or a lack of certain vitamins or nutrients may impair fertility as well. (see Natural Fertility)