Mucus plug

I am nineteen weeks pregnant and passed some of my mucus plug today, about the size of a 50p coin, yellow in colour. Called the midwife and explained, she seemed to think it was normal and if I have any more then to go and see my GP but seemed quite laid back about it. Has anyone else had this? FTM after long term TTC and feeling a bit anxious about it so wondering whether to go for a second opinion. 
Thanks :-)