Retirement is different for everybody, I took early retirement 5 years ago , initially did a bit of consultancy , have enjoyed every year with this year being my most content . Starting something completly new is not for everyone and I found that extending my then current interests worked very well . I'd always done a type of voluntary work , I extended that into helping to train new members, always been a runner now changed clubs and heavily into helping at parkrun and other activities.
One thing I've promoted a number if times on GOT is Walking Football. Our group of about 16 are all retired, varying degrees of fitness , men and women and we have a sociable chat over tea and biscuit afterwards. I'm sure there'll be a session going on somewhere close to you , it's worth searching for , whatever your current level of fitness is you'll be made welcome.
I don't think there's a magic bullet , as I said everybody's different and retired people don't suddenly wake up one day and suddenly start a new hobby out of the blue, but there are many opportunities out there from just spending a few hours volunteering at a local charity to extending current activities like walking into something more sociable with a local group.
Good luck mate, I'm sure you'll find some things to get you a bit more motivated and the negative thoughts from your head , sounds like you've already started making progress.
