New at this and struggling. Any suggestions?

Tell mom you can accept 2 calls a day, the days you work and 3 on your days off. Work days one short one in the morning, and one in the evening after dinner. Can you find a phone buddy for her? I had to limit my mother's calls too. However I also had a friend who doesn't work, and she calls mom every day just for 'girl chat'. Gives someone for mom to talk to, so she doesn't feel so alone. Also if there is a real issue, my friend will call me and give me a heads up.

Hugs, Sandra. I do appreciate how rough this must be for you.

There's that comment, which I can't attribute 'cos I don't know who came up with it, that when a person behaves as your mother is doing she's not giving you a hard time - she's having a hard time.

Unfortunately, while true, this does not make it any less miserable for you to watch.

And if you lost your Dad in January you must still be grieving too.

All in all, I should sigh heavily and write this year off as a real bummer of a low point. Your mother's anti-depressants won't have any visible effect much before Christmas but she should persist with them - it's not a radical change, more a gradual lifting of the darkest gloom that you can expect to see.

Meanwhile, turn your phone off when you're at work. Your mother is safe and has help at hand, so you really don't need to engage with her generalised unhappiness all day. You can always get into the regular habit of calling her during your coffee break or something if you're worried she might feel abandoned - set a timer for five minutes and ruthlessly say "got to go! Love you!" when time is up; and give the ALF staff a different number to call in case of emergency.

And, who's taking care of you?

"My mom is now pretty much my responsibility even though I have 4 siblings." Why is this the case? Are all of the other siblings far away?

Set boundaries about work calls. We've read here of people getting in trouble at their jobs because of the constant interruptions by their elders. And then stand firm with those boundaries.

What do your siblings do? Do they ever visit? Do they ever call your mother (does she call them?), so they get to hear her complaints, also?

"Talk to the staff at the front desk about that mom"
"I'll look into that mom"
"I'm so sorry that's happening mom, let me check that out and see what the solution might be"

I agree with not answering calls during the day. Alert the SW or DON at the facility that your mom seems to be having issues; they need to be extra solicitous and ask her frequently if she's okay. That's THEIR job

Once my mom called from her $5000 Ind. Living apt to say she had ants in her kitchen and wanted us to come right away. I told her she had staff to deal with that. She said she wanted US to do it, that the staff wouldn't do it "right". "For $5000 a month, they'd BETTER do it right, Mom" is what I said.

If there is a true emergency, ALF staff will handle it and call you. You can safely not answer Mom's calls while you are at work.

I expect your mother is in mourning. If she has been a complainer all her life, more complaining may be how her grief is being expressed. Or her declining cognitive skills may have her frightened Complaining about other things can be a form of denial.

In any case, it would be good if she could be redirected to get her needs met at the facility, and not rely on you. When you visit her it shouldn't be to solve complaints. It should be to have fun. Try to work your way out of the "receiver of complaints" role.

Why answer the phone? Wait until you are off work. Or is it an office phone and you can't tell before answering that it is her? Boundaries are important. Tell her very plainly when you are available. Consider whether this is new behavior or is it just harder now that your dad isn't there to be a buffer.
I know some don't agree with this but I find cameras very beneficial. If you can look on your phone and see her upright and mobile you can pick and choose when to react. There are wireless cameras. You do need Internet service for those to work.
It will take most antidepressants a month to six weeks to make a difference.
Make sure you have all your paperwork done for mom. DPOA for medical and financial. Make sure she doesn't have a UTI. Get a baseline neurological exam.
Depending on her complaints, perhaps the AL can help? Be sure to speak with them about her issues. Perhaps they have suggestions.