It is not clear what you have done, other than to access a joint account. If you were acting as a joint account holder, then the money is legally as much yours as it is your mother's. That is one reason why I do not recommend joint accounts.
If you were acting under the Power of Attorney form, then this is almost certainly improper, unless the POA form specifically authorizes you to take loans, which would be unusual. Under the POA form, you are required to act in your *mother's* best interest alone. It is hard to see how these loan(s) would be in her best interest.
You are most likely going to need to hire a lawyer. In answer to your specific questions:
1) It is not the fact of the number of checks or the amount, but the fact that they were not in your mother's interest and someone suspected that you were financially abusing your authority.
2) The money is your mother's. The bank cannot keep your mother's money. It can refuse to allow you to access it, however, without court authority, if it determines that there has been an abuse.
3) I think that you very well might need a lawyer. I would not want to do anything further without one, in your case.
I am licensed to practice law in the State of Michigan and have offices in Wayne and Ingham Counties. My practice is focused in the areas of estate planning and probate administration. I am ethically required to state that the above answer does not create an attorney/client relationship. These responses should be considered general legal education and are intended to provide general information about the question asked. Frequently, the question does not include important facts that, if known, could significantly change the answer. Information provided on this site should not be used as a substitute for competent legal advice from a licensed attorney that practices in the subject area in your state. The law changes frequently and varies from state to state.
If you think that someone suspects you of any kind of wrongdoing, I would definitely discuss the situation with an attorney. Also, I would not talk about it on the internet. Your discussions with your attorney are privileged and confidential. Your discussions here, not so much.