How to act around my boyfriend's mom.?

Hello everyone, I have been in a relationship with an awesome guy for about 4 months now. we get along great. I have an almost 2 year old son whom he is great with. he has met my family and my mom likes him a lot. he comes over talks to her and all of that. I have met his mom a few times and those few times have been rather uncomfortable. the last of those was a REALLY uncomfortable car ride with her. I'm pretty sure shes a nice person and all but i just don't know how to approach her. the worst part is he doesn't have any siblings around that i could maybe interact with. I tend to be a very shy person when i first meet somebody (especially my boyfriend's parents) but once they warm up to me i'm quite talkative. I don't just want to go to her house and feel uncomfortable. I want to be able to talk to her and actually have a conversation with her. I just don't know how to approach her. so any advice would be greatly appreciated. thnx