I think you should re-evaluate your thoughts. I use to feel that way, until I decided to say screw it, I am beautiful inside and out! Now I feel great about myself most of the time. I got this hideous burn mark on my face. But I know it is going to go away and my skin is going to be flawless in no time. You aren't ugly and fat. And if you are happy with your friends, they most likely want you. Your smile probably brings smile on their faces. You aren't ugly. When I was 15 i had so many pimples and I was chubby. Once, I got older, my pimples (they lasted about a year or year and a half), went away completely. And I lost a ton of weight through eating healthy and exercising. If you aren't happy with your body, then just change your habits. But in the meantime, you should stop criticizing yourself. Treat yourself with respect. If one of your friends was being put down at school by someone and being called fat and ugly, I am sure you would stand up for them, right? So stand up for yourself, and don't put yourself down! You can do it!! :)
I hope this helps you beautiful! :)
Depression doesn't have to be a 100% of the time thing for it to be very real. If you feel like it a lot of the day every day, or more days than not, it counts. Try googling the symptoms of depression and see how many fit you (I see at least 3 in this post, maybe 4). The Beck Depression Inventory gets at some symptoms like body image and self esteem a bit better, and gives a relative rating of severity.
Suicidal thoughts are no joke, and they alone are a reason to see someone. If you tell a psychologist/psychiatrist/therapist that you're upset about suicidal thoughts but have no intention to actually try it, they won't hospitalize you, they'll just try to help (some people avoid getting help for fear of being committed, but it's actually not as big of a risk as they think). During the two massive depressive episodes I had, I had intrusive thoughts of suicide, which were really scary. The reaction of the psychiatrist both times was, "Oh ok, are you planning on carrying it out? No? Ok, lets work on treating this".
It helps if you can get a healthier attitude about your appearance and weight, but depression can cause anyone to feel worthless and ugly, no matter how good they look. Exercising more (as long as it isn't excessive) is always good, because exercise does help with mood, will help you lose weight if you need to, and make you healthier overall. Try to get on a regular sleep schedule. Sleeping enough is really important. I know it's tough (I have trouble keeping a schedule, and I have Ambien to MAKE myself sleep), but it's helpful. And boys at age 15 aren't all they're cut out to be. More trouble when you're that age than they're worth most of the time, not that any 15 year old will actually listen to that :)
In all seriousness, though, please go talk to someone in person about this (preferably a professional). It's not attention seeking, and you deserve to not feel like this.