I'll add a little bit more to the story then:
The beginning of February, I was put on anti-depressants (Zoloft).
By April, I had stopped taking them.
All this time I have always been wondering whether my depression had truly gone: I was never sure.
So this time, it has come back, and I'm not sure whether it has been triggered by my loneliness or whether it has just come back anyway. Now I am getting more support online, I don't feel so lonely anymore, but my mood is still down.
So I suppose this is the reason why I'm asking if it is a chemical imbalance or not.

I know people have advised that I go to the counsellors. Last year (since I have restarted again this year) I went to the University Counselling Service and told somebody there all about how I was suicidal and she helped me. So this time, if I go there, I'm afraid I will have to have a session with her again. I'm even afraid of just seeing her or her seeing me: she will recognise me. If I started counselling sessions, I would be sure to see her sometime.

So I'm not sure whether I should go to my doctor (whom I have never seen before: he's my university doctor) or whether I should try counselling anyway and hope I don't see my counsellor from last year. I would find it very embarrassing if I met her. But I'm also afraid that if I go to the doctor and he puts me on anti-depressants, my doctor at home will see the records (it's all on computer), and he will know he was right (he advised me to be on Zoloft for at least a year). I don't know if the same patient's details are shared between doctors if he/she has more than one.

So for me, it's a difficult decision.

(Sorry this is so long.)