What should you do if someone is spreading rumors about you?

So, I like this guy at my school and after finally getting up enough courage, I told him. He acted really happy and said that he felt the same way so, obviously, I was really psyched when I went to school the next day. But when I got to school people were snickering and rolling their eyes and stuff so I got really self-conscious and asked my friend Danielle what was going on. She said that the boy I like (Eric) was telling everybody that I have AIDS. I was really upset and hid in the bathroom at lunch, and then faked a stomach ache and went home early. My mom doesn't know what's wrong and she's worried about me. I don't know what to do! Please help.