Keep a few things in mind:

All you can do is all you can do. Don't stress about stuff that doesnt get done. You're not paid enough / senior enough for that to matter to you (i assume).

If you're salary, working extra hours is sometimes expected of you but it should never be the norm. You go home when you've worked your full day. If one field tech (you) can't get everything done that needs doing that's on the company, not the field tech.

Its important to manage expectations and over estimate the hours that you need to complete something so you can be the hero by finishing early. Another important thing to do is to let your manager(s) know what will have to be dropped in order to get stuff done. ' You need me to handle the Server 3019 issue at Fuckwit Inc. sure no problem but just so you know it will mean that the firewall changes at Bitchplease & Sons won't be completed today.' Let them decide what to do.

Even if you do work late, do so within reason. And of course, if it's a proper fan+shit situation and they need all hands then do your part. But again, it's not the norm to work crazy long hours or extra days. You have placed to be (read: not at work).

It sounds like your managers will ride you into the ground if you let them so establish your boundaries.

With that being said it doesn't sound like a good place to work, you can do better.