Is my weight unhealthy?

I'm 17, 5'3" and I'm in the 90's. last time I checked I was 92lbs, but due to me being on the swim team I've gained more muscle but I have not weight myself. I can't ever seem to gain weight, I would eat around 3,000-4,000 calories and day and I'm still the same. My family and people at school tend to make fun of how skinny I am to the point where I just stop wearing sleeveless shirts to school so that people don't see my arms. I've never experienced any problems or anything with my body, but people like my sister and a few of my friends tell me that my body isn't normal and that I wasn't supposed to be born this way. It makes me sad because I've tried everything, including diets and working out, and nothing seems to ever change.

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no I don't starve myself, no I don't eat unhealthy, and no I'm not obsessed with counting my calories. I would only count them since I wasn't sure at first if I was taking the right amount a day, and I thought taking in more would help me gain weight.