What To Do?

So I've been thinking a lot about what is going on inside of me. I have a lot to be grateful for, at least I am told that all of the time. I am going to be a grandmother, my fourth child is graduating from high school and going on to college, I have a mother a husband and a niece who count on me and two children still at home who need me. But does anyone think about what I need? Does anyone consider how I feel when I am told: "You ask too many questions!", "People judge me by the way you look.", and my favorite when I disagree with anyone in the family; "Have you been taking your medication on time? You don't seem to be thinking clearly."
According to my family, I am only exhibiting well behavior when I sit back, nod and smile and let everyone do and say as they please. I am not allowed to disagree or express my feelings. Apparently, my feelings are not real because I am mentally ill. If I were not ill or my medication were working properly, I would see that everyone should do and say as they please. Basically, my feelings are invalid! Nobody seems to understand that my feelings of inadequacy date back to my early childhood and are only compounded by my present family dynamic.
I have been sitting here all evening trying to come up with a reason to continue living. I cannot come up with a good one. I am nothing. I will always be nothing. So... what to do? What to do?
I cannot decide whether to take pills again or stick with my original plan of gassing myself in my car. I am leaning toward the car thing. Here is what would make it perfect:
1. Park by the river in the evening right before sundown.
2. Get out and run a hose from the exhaust into my rear window.
3. Either shoot some heroin or light up a nice joint. I have never done heroin so I'm kinda thinking this might be an opportunity to experience an incredible high before I die.
4. Turn on the radio, The Moody Blues or Pink Floyd.
5. Watch the sun set as I wait for death.

Now... to find the perfect time.