What couls this be? TMI

Okay I'm 18 weeks and 2 days. The last few days to about maybe a week I've had vaginal discharge that looked kind of snotty (best way to describe it). I've read that the mucus plug will/can look like this and can also regenerate itself or come out months before labor. So my question is could this be the mucus plug or what? It's not a STI or STD because Monday I was tested again and all came back negative so I know it's not that. Any help would be great!