Problems with mood

I know there are quite a few people on here that have had struggles with mental health. I'm wondering if anyone could advise me from their experiences. 

I've always had a slightly up and down mood, even as a child. But never to an extreme and never long lasting. I've always been easily irritated and angered which I would assume is my autism. The last few years I've noticed more and more periods of low mood. I think part of this may be due to lack of friends. But it tends to go away when I'm busy so I've never been too concerned.

At the moment my mood seems to be lower and longer lasting. It does still go away for periods when I'm at work and I feel fine. But I'm feeling like I'm more easily irritated by others at work at the moment and I'm worried about this getting work. In the evenings I do feel really quite low. It's a very heavy feeling and I have no idea why. Could it be depression? Or would I feel like this constantly if it were depression?

I know I should probably go to the doctors about this but I know I won't tell them. I don't know why but I've never been able to admit to low mood to an actual person. This is the only place I've ever been able to admit to it. I don't think I could even write it down and give it to them because I'd still have to discuss it.

The last time I went to the doctor they said to have a think about whether I wanted referring about my anxiety for a talking therapy or medication. I'm really not sure I want this either. But at the same time I'm not sure the anxiety and mood can carry on and I'm worried about it all getting worse.

Any advice?