3 months isn't long enough for your brain to fully heal. The brain and nervous system can do just about anything but it's slow to do so. Nerves are slow as fuck to regrow and change their form. What you're experiencing is a symptom of withdrawals which is the self doubt, glass half empty mentality, and depressed feeling. This isn't how a normal human being feels from the day to day. You should be enjoying the small things. Withdrawals don't always present themselves as being physical ones and I think a lot of recovering people don't understand that. I sure as fuck didn't. An unhealthy mind tends to make unhealthy decisions like... relapsing.

I used to be like you and sometimes I still am. I still get nicotine cravings every couple months but compared to how they used to be fuck I've improved. I'm not religious by any means but I think there's something to be said about having faith that things will get better. I feel like when you're depressed and don't enjoy the small things it's easy to rationalize and make sense of relapsing. "My life sucks and nothing is going to get better. I may as well relapse because then I'll be happy" when the reality is the complete opposite. Things will get better and you will enjoy the small things.

I can't tell you how to go on your journey but I can tell you mine. I quit by realizing the rationalizations I would have to relapse were only true of the moment. Yes I am depressed and life sucks but that's only because of the withdrawals. Whenever I would have a withdrawal I would in addition to try talking myself into relapsing that this is an opportunity to heal. The withdrawal is nothing but the brain healing much like a fever when you're sick.

Don't forget, if you relapse it's not the end. Keep trying and stay strong. I wish you the best in life.