Here is what I do that helps:
1) Weekly video call with the same small group of friends. We started doing this early in the pandemic and now we do it even when none of us are really feeling it (those calls are short). But we have stayed committed because even when we are all kind of sick of and annoyed with each other, it is keeping us connected and helps with the isolation and the parenting stress. If you can find a way to make this happen, I highly, highly recommend. Try scheduling for 8pm after the baby goes to bed.
2) Join a virtual gym. I got a subscription to Barre3 and do barre classes in my living room a few days a week, plus go for runs while my DH takes solo parenting time at least a couple times a week. If I don't feel like running or working out, I go for a walk. If my DH is busy and I have to get out of the house, I bundle the kid up in our stroller sleeping bag thing, hand her a snack and sippy cup, put on my headphones, and just walk around our neighborhood while listening to a podcast. Bonus: sometimes she falls asleep and when I get home, we can park the stroller somewhere quiet while she naps and I get a bonus break.
3) Try one of the therapy apps. Better Help is good. Or call your insurer and get a list of approved therapists and call around to see if anyone is taking new patients and has tele therapy.
4) Do a bedtime routine for yourself. I like to lie on my acupressure mat for 20-30 minutes while watching TV, then take a bath with lavender Espom salts, then do my skin routine and read in bed for a little while. No screens. If your baby is sleeping 12 hours at night, this is a great time to get in some recharge time just for you.
It will get better when the weather warms up. You'll be able to get outside more, your baby will start walking and be more active which is a great distraction, and there will be more opportunities for outdoor socializing (and exercise classes!). This is just a very tough time with everything hitting at once -- peak Covid, February weather, residual hangover from political crap, and probably some normal adjustment to motherhood for you. Check out this article on "matrescence" from Alexandra Sacks:
https://medium.com/@alexandrasacks/matrescence-what-is-it-bea6aa0450d0. It helped me understand the life altering shift of becoming a mother in a way that is bigger than the usual discussion of postpartum depression or maternal anxiety.
Good luck! You aren't alone -- a lot of us are right there with you.