13 weeks, having cramping and losing pieces of plug

So I went to work today and after standing for 5 hours straight I had lots of pressure and cramping. I don’t get any breaks to sit or anything and this use to be perfectly fine with me before pregnancy. I feel very heavy in my abdomen , I don’t really know how to explain it. I just went to the bathroom and saw a piece of my mucus plug , very gelatinous. This is not my first pregnancy so I know what it’s to look like. Has anyone had a similar experience and went on to have a healthy pregnancy?