You’ve mentioned rodents. Any poison out for rodent control?
ETA:
This could help with the flies and cheer you up!!
The exterminator put out poison. The flies seem largely to have disappeared as suddenly as they came.
I think I will call H and see if some kind of visit can be arranged.
Again, this option is limited by bad local transportation needs, but one extra out of the box (well, or not so out of the box, as it’s CATS) is to see if there’s a local Cat Cafe you could visit.
Even here in Colorado Springs, which is sadly lacking much in the way of variety of businesses and shops for a city of it’s size, we finally got one, although it was so popular they had to upscale and are temporarily closed at the moment. It’s never a perfect fit, but it hits the get out, do something, and if one nearby-ish is linked to a local shelter like ours is, it’s a three-fer of good results.
Based on your profile location @DocCathode, here’s a yelp search:
So looks like you have more choices than I (but not a ton), although given the size of Philly, I can’t say if any are close.
Thanks, I shall give the link a look.
I’ve been there (and I’m still there) and it sounds like your like me and suffer from depression. Absolutely no shame in that AT ALL!
During Covid I was hospitalized, got a bit better and then my father passed and 3 months later I lost my job…. It isn’t the end and everything improves.
During all that time I had times where I couldn’t even watch the movies I loved or play the games I did as I couldn’t focus. My mind was (and still is) kinda all over the place. Trust me when I tell you things will calm down but you have to take some time for YOU. Self healing is key. If you can’t change it at this moment, don’t worry about it and look after YOU!
Now as for the rodent, nothing to worry about. (I can help you with that too. Trapped a few and saved and released a few. 
Don’t give up, friend. I may not have been on these boards in about 20 years but DM me if you need.
Now that the flies are gone, watch out for frogs.
If an old guy with a beard and a staff comes along, let his people go.
Back when I had mice getting into my basement I experienced a sudden onset of flies after a mouse died. They must have used the carcass as an incubator. Imagine going down to the basement and seeing a clothesline lined with identical flies. It was something out of a horror movie. They got smoke bombed that night.