Hello Little Joe,
I'd like to make you feel welcome here at the Forum, we are a friendly bunch.
Going from full-time country life to retirement in the big smoke is a huge change. Add having health problems & it's natural you may find yourself struggling.
You didn't say what health issues you were facing (please don't feel you have to) so I will offer a couple of suggestions.
Many different health problems have support group/information web pages which include useful links & places where people can get face to face support from peer groups etc.
Most hospitals have patient support areas on their web pages, which may be able to put you in contact with support groups.
Also a good start point can be your GP, they deal with mental health all the time & you could ask for a referral to a psychologist to talk things over with. They can also determine if medication would be helpful for you.
As to finding things to keep yourself busy & more importantly engaged, are you interested in volunteering or do you have hobbies/interests (old or new) for which you could join a group. Many councils have information on local groups which you could join or events you could attend & there are plenty more which maintain an on-line presence as well as face to face. You could also check if there is a Men's Shed in you area.
Just a few starter idea's. Of course there is also the BB forums. The social section has a wide variety of topics/interests you may enjoy and then you have this your thread, which is whatever you want to chat about.