Constant fatigue after going out + socialising

Does anyone else get fatigued and a headache after going out like into shops and when you've been socialising?

I get this all the time and it really puts me off from going out. I go in to it with a positive attitude as well and it makes no difference. I've been told it would make a difference but it hasn't. It's so frustrating because I just want to get on but because I went out this morning I'm now feeling extremely fatigued, dizzy and I have a headache. I don't know why this happens. It's nothing serious, I've had tests at the doctors and nothing was ever found and yet here I am feeling like I've just run the marathon....

I don't know if it's the autism or the anxiety... Or maybe a bit of it all together?

I do know though that I hate getting like this. I was diagnosed with ASD when I was 14 and though it's been over 10 years since my diagnosis I don't really know anything about ASD and how it affects my life. 

That's why I've joined here really to try and find out more about it. Hopefully then I'll be able to better manage how it affects me. 

This fatigue I get when I go out and do things has already cost me my job. I waited so long to get a chance at work and after a few days I was practically bed ridden. It's crazy. 

I'm in bed bed now, absolutely exhausted, and feeling like death. Wish this wouldn't happen I really do. It's fine when I stay in my room but when I leave my comfort zone all hell breaks loose and I'm left feeling like I've got a flu bug thing. 

I did say to the doctor but she won't give me anything because it's not real. She thinks it's a mental thing and "phantom" pain and exhaustion. No use at all. Rest helps but it takes time to recover.

Sorry for the rant. Not really how I wanted to introduce myself to the community. I'm just tired and feeling run down.