Please don't feel self conscious. It's not a big deal. There's much worse things you can be called than 'spotty'....
"racist, homophobic, rude, shallow, vein' etc....
A lot of it is just hormones. I used to have terrible acne and now it's all cleared up. It's very common and its nothing to be ashamed of.
My ex had really bad acne and it used to get him down, but it seems way worse to you than it looks to anyone else. You really stop seeing it when you spend a lot of time with people.
It could easily be dietry. Being horribly underweight is probably a large factor..but sometimes it's just genetic! You may grow out of it.
Chocolate is a huge cause of acne, fizzy pop, high in saturated fat, not enough fruit and veg...etc.
Make sure you're eating a healthy balanced diet, drink lots of water and that's all you can really do....
If I were you I'd probably look online at some anti-acne food.
Other than to keep your skin clean, and don't use anything that will irritate it.
I used to use murad when I had acne and it cleared it right up.
Also, don't stress! Stress also causes break outs!