I am the same way, but I would definitely that it's easier for an Empath to be happy, especially when we just feel everything so differently and realize what a blessing it is. Other people are stuck feeling and living completely different lives and I know that it has to be annoying for some people who are in a bad mood or are more negative to be around people who are happy and genuinely love life. I personally don't want to live any other way and I've decided that I want to make others happy or at least help them find happiness in themselves if I can't do it. What I do is not try to let my positivity take control of a conversation (although a lot of times it's needed). I usually let the other person set the "mood" and go with it. But there is definitely a difference between someone spreading negativity and just setting a more relaxed mood, and i would be very careful not to associate too much with people who do nothing but talk negatively about others or their life, instead use your happiness to give them something to be happy about. Compliment them and the good qualities you see in them or the person they talk bad about, and it lightens the mood almost instantly. This usually works for me, but you have to be careful about not being too in people's face while using it. I hope I didn't give you anything you didn't want/ wasn't expecting lol.
I think there is NOTHING wrong with being positive and happy. It's healthy. Those who are not so much and more negative, I think that's their issue. We can't control how they feel, but we can control to not be around it if it's going to bring us down. Life has so much to offer if you take up on it. Those that don't, let them be and let them drown in their sorrows. Sometimes I feel that people who do have a problem with the positivity and happiness from you, is their own jelousy and insecurities. Where they say "I wish I can be more like you" well you can, they just choose not too. They look at all the wrongs versus all the rights. Have you ever met someone going through a hard time and they always have a smile on their face? They don't allow that to bring them down, they see it as a life obstacle and one day it will be over. That's what I strive to be more and more each day. For me personally I'm done with those negative people and I can't help you be happier like they ask. And I really tried over the years with people, and in the end my energy was just sucked out. I think with our gift it is harder on us to be positive and happy when we can see and feel so much sorrow in this world, and want to help.I really don't think you should tone it down. This is who you are. Don't change yourself because someone can't handle it, it really isn't fair to you. All you can do is change how often to be around these people or look for new friends.