You are not alone.
Your first contact should be with your GP (doctor). They will be able to refer you for mental health treatment. This might be Cognitive Behavioural Therapy (CBT) or Interpersonal Therapy. A trained psychologist will assess your needs. I know this, because I have been through it myself.Below is a list of mental health charities.
Having looked at their websites, I would recommend:
Samaritans for someone to talk to (by email, phone or post)
The NHS site for practical advice
Turn2Me for online support groups
Samaritans for someone to talk to (by email, phone or post)
The NHS site for practical advice
Turn2Me for online support groups
Time to Change for advice and links to self help sites
Elefriends for peer support