Really unhappy in my relationship

I've been with my partner for 3 1/2 years now, we had our son in June but ever since my son has been born, our relationship has went downhill, we argue constantly, I feel he shows no interest in me, and when I talk to him about it he just puts up this big defensive wall and says I'm making things up. I'm not pulling these feelings from nowhere. I am considering leaving, I'm so unhappy, I feel I'd be happier without him, he never compliments me when I'm feeling unhappy about my postpartum body, he never give me any confidence booster, it's like he doesn't give a shit, we ain't had sex in a year. I have just turned 20 and I feel if I stay with him any longer I am wasting years of my life. I really need advice, he just doesn't understand how I'm feeling😩😩