The best comparison I have found is to compare it to diabetes. They are both an imbalance in the body to correctly produce a chemical needed to function on a healthy level. Just as we don't expect a diabetic who is insulin dependent to just "get over it" and live without his insulin, it is equally insensitive to expect a person dealing with depression to just get over it and pull themselves together.
My mother suffered from depression pretty much my whole life. She was hospitalized several times when I was young, yet I really didn't understand what depression was until I had to live with it. Depression isn't a "mental" disorder so much as it is a "chemical imbalance" and unless people are willing to think of it that way, there isn't much of a point in explaining it. The brain isn't able to correctly produce and use the chemicals it needs to function correctly and the result is depression, anxiety, social phobia, paranoia, etc depending on the individual person. If not treated, there are also effects on the body. Severe fatigue can result, people can have panic attacks, have heart attack symptoms, appetite is affected, nausea can result. None of these things can be "fixed" by the person simply by "getting it together. It is a physical/chemical illness.
I have always said that I don't consider myself "mentally ill," I am "chemically challenged."
The thing to remember is that depression is in no way a personality or charactor flaw. It doesn't reflect on you as a person. You aren't "nuts" or "mentally ill." You have an illness that you are seeking treatment for. It's likely not permanent, and once you are on the meds long enough for them to have corrected your brain chemistry, there is a likely chance that you won't need them again.
Unfortunately, for many people, this is too much to understand and you won't get anywhere. I feel lucky that I have a wonderful supportive family, but the best support I have comes from my friends who also live with depression. You may be surprised as you begin to talk about your experience with your mama friends how many of them have walked the same path.
Good luck and keep coming here. We understand.