I've never read/heard anything about it meaning you have a thinner lining. That can be a side effect of Clomid, however. That's one of the reasons my OBGYN put me on Femara instead because it has less side effects like drying up cm and thinning uterine lining. I would just try out the Mucinex, but make sure you drink lots of water for it to work properly. Some women don't ever notice much cm, but you can have fertile cm without seeing it. I only had one day of it this cycle, on OV day, and I had one day - I think maybe 5dpo - where I had a bit of white thicker cm, but other than that nothing this cycle.