Whether you are gay or not, no one should be calling you that to begin with, people have always got something bad to say, no matter who you are, what you do, or where your from.
The best thing to do is to keep your head up and believe in yourself, obviously they want to hurt you in some way, dont let them win :)
My best advice to you is the old advice of sticks and stones will break my bones but names will never hurt you. Your sexuality is your business and it doesn't matter whether you are or are not a homosexual, it matters that you are happy with yourself. People will always be ignorant, they would call you purple if they thought they would get a rise out of you.
If you feel that you need help with your sexuality, there are many places you can go, counseling, the Samaritans, the internet is a good source of assistance, there are lots of charities out there helping young people (and people of all ages) with issues of sexuality. If you are young, there's no rush for you to know whether you are gay or not, if you're older, it also doesn't matter, life is long, and you get to make the big decisions for yourself.
First of all you must be aware of what you are, if other people call you gay and you know it from your heart that you are really gay, then be proud because the whole world know that your gay, and being gay is not a disadvantage of being human, instead, it the most colorful, meaningful life. Be proud that your gay because the future depends on you. This is the only thing that I'm going to tell to the people who always discriminate gays, "they are the dogs barking towards the moon".
If you are gay then it shouldn't matter be proud! :D If you aren't then don't make a big deal out of it, even if you were it isn't a bad thing to be, so just ignore that shit. And people shouldn't be calling others gay like it's a disease, it's not a bad thing.