Hi there.
This is a tricky question, because it depends on the situation! I don't know if you see the lively people change when you enter the room. If you don't, then don't worry about sucking the liveliness out of them.
If they do change, or quiet down, it could be something as simple as that they see you as a serious person and know they should tone it down, if the situation calls for it. Or it could be something else entirely, as in- do you smile when you enter a room? If you are nervous enough and quietly enter a room without waving to a friend or smiling, people are conscious of negative feelings/emotions. If they get that you are sad/upset, THEY won't want to affect YOU with their liveliness.
Try smiling, and see if that makes things better. Smiling is contagious! This doesn't mean you have to be energetic and lively too. All the best etc.