I'm going to advocate for sticking it out for a longer period of time, say, 9 months to a year or even 18 months. Yikes! I know that sounds like there will be little soul left, but the truth is, if you begin NOW to scope out other openings, it won't be that much longer until you find something new and orders of magnitude better.
There are two things missing here. One is ...what is your compensation? Are you being paid so well that you can simply suck it up, bank some money and maybe have the coin to take a real vacation between jobs to do some soul restore? If so, it is well worth it to hang on a few more (or say ten more) months. If the bank is good, you should be able to supplement your sh*t job with running, fun with friends, and get by, not indefinitely but for long enough to deal with my second issue:
Why didn't you make the effort to SERIOUSLY check out the organizational culture, norms, workday realities and workplace soul suck that you are now complaining about? Truly, some organizations will hide this from you, and maybe you did make a concerted effort to learn about the realities, but it's my experience that when we want something badly enough, we don't look for all of the downsides, we just plunge in. that's ultimately it is often possible to ascertain just how bad a workplace is, going in. You can interview people who have left, ask actual questions about the workplace culture, norms, boredom level....go online for reviews. i assume that you did these things but if not, you're going to drill down deeper next time.
In all my time hiring, I saw relatively few people who didn't have an OOPS job or two. If you decide to move on, cut your losses in a way that leaves no bridges burnt. Simply say it's not a good fit, thank them for whatever they taught you, but no need to be a jerk about it -- which is sounds like you would never do anyway.