Mucinex vs Robitussin

So, I’m on my 4th round of Clomid. Had a check up with my Dr. yesterday and I told him I didn’t feel like I had “fertile mucus” since the 1st round. My blood work is great, I’m ovulating but I don’t get the EWCM. So he told me to drink Robitussin. I’ve seen where women take mucinex and always wondered why, until now. Anybody had to do this too?