Coworkers want to hang out a lot

I (24f) started at a small nonprofit job about 7 months ago. It's full time, fully in-person in a small office. It's only me, three other coworkers, and my boss. I get along decently well with everyone and we're all friendly but I feel like I don't fully click with my coworkers and don't want to spend that much time with them after work.

About two weeks ago, we hung out 3 times in 4 days (two times after work and once on the weekend). We went out to dinner again this week and my coworkers wanted to go to the mall afterwards but it was 6:30 and I was tired so I left early. They looked at me confused as to why I was leaving early. I'm an introvert and I need alone time. I'm also getting sick of spending so much time with my coworkers.

I have a life outside of work. I have my own friends, boyfriend, and family that I want to see other than my coworkers. My coworkers are all nice people and I know they have lives outside of work but they really put a lot of emphasis into their work friendships. Has anyone gone through something similar? I don't want to be rude and decline all of their invitations but I'm just getting tired of them.