My sister was TTC #1 for 3 years then her Dr suggested she take folic acid. After a month she got pregnant. I believe it's an OTC supplement, I don't know how it works or if it's common but she was willing to try anything before trying the expensive treatments.
It thins out your cm. if you never have ewcm at ovulation, it helps. Thats all robitussin does though. I used it while on clomid bc.it can dry up your cm.
I've heard about robitussin working for people. But I personally do not know what it does or how it works
Gnc fertility I've had a friend that took it 3 times a day and got pregnant!