POA for my mother who was placed in nursing home 1 week ago. Am I responsible to pay her bills when there is no money for them?

No you are not responsible for her bills as POA. It has been recommended here that you don't even contact creditors. The calls you are probably getting are from 3rd party collection agencies especially with credit cards. I would, one time, inform them when they call that Mom is now in a NH with Medicaid and because of that, there is no money. Refuse to give them any info concerning who is POA. Tell them that it does not matter who the POA is because Mom has no money. POA is only responsible to pay bills when the principle has money. POA is not personally liable. Either are children. Then you tell the collection agency to not call again. Keep a record of who called you. Because if they call again, you can tell them its harassment and report them to the FTC. Send bills back with "person no longer lives here". After a time, don't even bother. Do not change Moms address to your own. I thought that would be a good way of getting rid of junk mail. I would only have to notify the people I needed to to make the change. Wrong, somehow, someway the junk mail people got the new address. I am still getting mail in her name and she has been gone 3 yrs. I was told by the PO it wasn't them it was the utilities and the utilities said they do not give out personal info.

I was a Collector for private companies. The FTC rules for us were not as strict as the rules for private Collection Agencies. These agencies have bought Moms debts. As such, they have no back up just an amount. The collector works on commission so he will say anything to get the money. Not all legal. Now utilities are a different thing. These can be turned off for nonpayment. So, if you are living with Mom, and the utilities are behind, then you could set up payment plans until you are caught up. Since you are disabled, they may be able to help with discounts. If you don't live with Mom, then you may just need to turn everything off at her home.

If Mom has money in her account after the spend down, this cannot be used for bills either. It can only be used on her personnally.

No, you do not need an attorney but you decidedly DO need to know what you have taken on and what you are doing and what the rules are. Please get a book on it. There are many. One is free and is put out by the government; wish I could remember where to tell you to get it. But it will be online.
Now. Basically a Financial POA is the one who is responsibly for paying the bills when the person who appointed them cannot handle this any more. NEVER comingle YOUR money with their money. Your money has NOTHING to do with them or their bills. Absolutely NOTHING. Be certain that anything you sign FOR them as their POA you sign using both your names. Let us say you are Joanie and they are Jane Doe. You sign all contracts and bills as Jane Doe by Joanie as POA, or by Joanie under POA. You are acting for them because they cannot and you are acting with their funds. DO NOT GIVE ANY OTHER ENTITY POWER OF ATTORNEY TO GET THE MONEY. In fact, you can give them legal rights to withdraw fees from the accounts, but if there are old bills they could empty said account, so do not do so.
If bills come simply send a letter signing yourself as POA saying there are currently no funds to pay these bills. If there ARE funds to pay bills then you are beholden to pay them for the person you are power of attorney for.
I do think that you have not enough knowledge, so were I you I would go to an Elder Law Attorney, perhaps the one who drew up the papers, or another, and say you do not fully understand your duties.
You should also be keeping folders with all bills, copies of all checks to pay them, letters from entities or creditors. You should be keeping an account book of what comes in each month and what is paid out and a copy should go to the person whose finances you manage if they can understand it.
This is not a things to take on lightly. If you are not up to it then someone else, even the state can be assigned to handle it. You can resign. But do not do it unless and until you understand it fully and can do it well. A mistake in signing COULD make you liable for bills. So pay for that attorney and it can be paid from the account of the person you are managing, and an hour of time will give you a lot of information about what you need to do, what you are taking on, and how to do it.

No! Please do not pay them any money out of your own funds. YOU are not responsible! Tell them your mother is in a NH and can not pay the bills,