Could also be bacteria vaginosis which is also common in pregnancy due to an imbalance in Ph levels and is very similar to a yeast infection. I just recently had the same problem and received medication. When you're pregnant your body goes through a lot of changed very quickly and that can cause an imbalance in your body. I am also 5 months.
I had that once and it was because I had a yeast infection - but I just didn;t know it. It wasn't until I went to the doctor for other symptoms that they checked and realised that;s what it was.
Do you also have a thick lumpy discharge? Or does it itch or hurt in your vaginal area? If so it could be a yeast infection, which is very common, especially in pregnancy. Either way, it's something to speak to your doctor or midwife about.