How does one limit the amount of overthinking?? 

I’ve always dealt with some type of anxiety but right now I’m overthinking just about everything, I mostly overthink my relationship majority of the time. I know I’m overthinking but I can’t get my mind off of it. My GF will tell me to stop and try to reassure me of something but it’s like I’m stuck in my head and I don’t know how to get out. I quit smoking weed to see if it would help and it actually helped a little bit. My job is shitty right now so maybe it’s stemming from that? I have to believe I’m not the only one that’s going through with this type of stuff. I’m dealing right now and that’s what I do, I deal with stuff and keep it in and try not to bother people with.