Please note that you need not ever go back to the property in order to manage the delivery and receipt of your mail deliveries, which is now the source of your primary problem. You need to immediately go to any Post Office and complete a Change of Address Form.
Then, you must give the completed Change of Address Form to a Postal employee (or drop it in a mail box), and it will be sent through the system so that your mail will be rerouted from your old address (at your parent's house) to the new address you will list in the Change of Address Form. This process will occur more quickly if you turn in the Change of Address Form at the Post Office for the zip code for your old address. The sooner you get this done, the sooner your Mom (or anyone else at her address) will no longer have access to your mail.
Next, unless your Mother can prove that she has a Court Order (or your permission) to do so, then her act of knowingly opening your mail is often a crime under both federal and state laws. On the other hand, you must be able to prove that it was your Mother, and not someone else, who knowingly opening your mail without authority to do so. Such conduct should be reported to your local Postmaster General's Office and/or your local law enforcement personnel.
You, of course, may be asked to demonstrate why more than seven months have passed during which you have failed to simply complete a Change of Address Form to reroute your mail. Such failure could be construed as contributory conduct, on your part, which gave authority to your parents to manage your mail, since it appears that you had abandoned abandoned your mail (along with any expectations of privacy related to same) for over seven months.
Next, if your Mother obtained sensitive, private and personal information from your abandoned mail and then told that information to others, there is nothing illegal in her doing so. If your Mother knowingly opened your mail (without a Court Order or your permission to do so), in order to obtain sensitive, private and personal information to then tell to others, in order to embarrass you (or to otherwise cause you harm), then such conduct could expose her to civil liability. Any judgment you may obtain in a civil claim against your Mother, for such conduct, would be paid from your Mother's assets (including your father's assets, if they are still married).
The answers to these questions can best be obtained via your personal consultation with an attorney licensed to practice in LA who is familiar with the legal issues above described. You might be required to pay, in advance, an agreed upon fee for the attorney's consultation. Make sure to confirm with your attorney, before you begin the consultation, whether or not you will be charged a consultation fee.