Advice on overthinking

All i do is overthink. Can someone give me some coping mechanisms??? Because it’s really messing with my head and starting to affect the relationship. I’ve brought it up twice to him (we’ve been dating for about three months now) and i feel like he’s slowly getting annoying and losing interest. Would i be feeling this way all due to just anxiety or is there usually a reason? How can i become more carefree??!