The problems with your mother most likely aren't related to the subject of this article: mothers who get jealous of their daughters. As an adult child who lives with your mom, you've put yourself in a situation ripe for conflict. It's one where old patterns from your childhood come into play, and your mother once again sees you as a dependent youngster and not a mature, autonomous grownup.
As long as you're under her roof, expect your mom to undermine your decisions and see you as incompetent. Instead of focusing on why she behaves the way she does, you would be much wiser to look in the mirror and ask yourself: Why did I put myself, my husband, and my son in this situation? While you may have practical reasons (you lost a job, you need to save up money for a down payment, etc.), you must appreciate that you had other options but chose this one.
You may be wanting to re-visit your childhood in the hopes of fixing the past. You may be unconsciously hoping that this time your mother will be the loving and nurturing parent you longed for as a kid. There may also be something in your life that you're trying to avoid and your mother's house is serving as your hiding spot.
Dr. Robin Smith says, “Adulthood is to finish the unfinished business of childhood.” You can't go back to fix the past, but you can use what you've learned from it as a guide to move forward. Since your mother is in therapy and on medication, she's in good hands and is getting the professional help that she needs. Leave her up to the therapist and concentrate on yourself, your marriage, and your son. If your struggles with her persist, call the therapist and ask her if you can join in on one of the sessions with your mother to discuss some issues.