It’s been 6 weeks since I left my job and started working full time on my side projects.

A few things you can do:

• find a co-working space and go there for a few days in a week
• if you don't want to spend money on these kinds of things, just go to a coffee shop, and spend a few hours there
• you can also go to public libraries, but I don't think those places are good for finding some company :D But if it's ok if someone just sits next to you, you can try this as well
  And the thing you've already done: join online communities, where you are never alone :)
  Some occasional events you can also give a try are meetups. Check out this list, maybe there'll be an Indie Hackers meetup somewhere around you where you can meet other fellow Indie Hackers: https://www.indiehackers.com/meetups

You are not alone, it's just your "coworkers" not sitting next to you :)

Can you also share what are you working on?

I think that working alone is great for productivity. You shouldn't be too hard on yourself, after six weeks, especially if you have years of work environment experience, it is normal to feel lonely but you will get used to it.

My suggestion is to work (alone) when it is time to work and harness the productivity to have more time for hobbies where yiu can spend time with other people.

In coffee shops and coworking spaces, you could win loneliness but reduce productivity and probably for low quality interactions.

Working in public helps, as does spending more time outside.

Curious to hear why you decided to leave, and how the lifestyle has been outside of a normal job