I am currently 39 weeks +2 days pregnant. Me and my partner have just took the dog out for a walk…

I am currently 39 weeks +2 days pregnant. Me and my partner have just took the dog out for a walk and when we come back I went to the toilet and found a large clump on discharge that was gooey/slimy and clear in colour. Could this be the start of my plug? Also I've been having period like pains and back ache for 8 days now. Hopefully this could be the start of things. First child so just need advice.