Can’t study like before

I used to be good at studying, i had really good brains, but after changing cities and having troubles socializing, i focused a lot in people and my problems and i changed dramatically. i can’t concentrate on my studies or study for a long time even after trying a lot. I become stupid, i don’t know what to do or what’s the cause of this. It’s been years and i am failing at university i know i can do better than this.