I truly feel like I'm overreacting

I've got a perfect life, my parents are still together and love each other, I've got an adorable little brother who loves me, my family is in a good state, no problems there.

I've not amazing friends who are there to support me, who understand me and don't judge me at all. I could go to them with anything, and they would be there to help me.

I'm doing okay in school, I've always been a pretty okay student, so that's not a stressful thing for me.

I've got insecurities about my body, but they're not that big of a deal to me, I couldn't care less about what people I don't care about think.

Yet, I'm still so anxious and sad all the time.

I don't give a shit about what people say, yet I'm so anxious. I've got no reason to be, it just comes out of no where and fucks me up for the rest of the day.

I've got no reason to be sad, yet here I am. People live worse off than me and push through it, and I've a life people would wish to have and yet I'm so... this.

The only problem I have at the moment is my ex and I broke up 2 weeks ago, but we're on good terms and it wasn't a bad break up in anyway, in fact it was mutual and left me feeling happier than I had in a long time.

I don't understand why I feel this way, why I'm so ungrateful. I've got such a good life, yet I'm here feeling so anxious and depressed constantly. I don't know what's going on.