I'm not sure I understand; how could one not be thinking about things constantly? If I try to just sit there and think about nothing, it doesn't work. The only time when the thinking has stopped for me is while under anesthesia.
For me I day dream all the time. I don't think about anything when I play guitar. I don't think about anything when I do the dishes. I don't think about anything when I'm laying in a hammock looking at the sky. I don't really think when I'm exercising outside of "this is hard!".
Even when I'm dating someone she'll ask "What are you thinking about?" and more often then not the response is "literally nothing."
So yeah, it's definitely possible to not think about things. Maybe it's worth the cash on a therapy session just to double check? https://www.betterhelp.com/ Is a good source.
To me this sounds like the equivalent of a tooth ache for your mental health, better to get it checked now then wait.