Struggle functioning when stressed

Hi, I'm new here. I was diagnosed with ASD when I was 6 but haven't really ever understood it as no one has really told me about it. I had some support as a child but now I'm an adult I feel like I'm all alone with it. 

I noticed when I'm stressed I struggle to function. Some days if I'm stressed I forget to eat and drink, I can't go out and I'm too anxious and overwhelmed to answer the phone. Though I never like to answer the phone anyway.

How do you cope with every day life and keep functioning? I'm nearly 30 and the more time goes by the more it feels like I'm failing to cope with the hassles of every day life. 

I don't know what to do to help myself. I'm really at a loss on what to do next.