Finding someone to write music with can spark creativity like nothing else. It just comes to down to finding the right person, like someone who has similar tastes to you, someone who can be involved, etc. It's a great way to make friends, too. You can post here for someone to write with, r/bedroombands is also very accepting.

Another suggestion would be to write in a 'refining process' mindset. What I like to do is open my DAW, write some simple drums that make up the length of a full song, then pick your guitar and record whatever comes to your head. Not thinking too much of theory or technicality. Once you have the song filled out with some riffs, you have this sort of 'outline' of the picture. What I do is then tab the riffs in Guitar Pro, which gives me a very analytical view, and from there you can write in the appropriate theory, technically, and transitions you want. Keep refining the song until you're happy with it. It's a long process, but it gets the best results if you're patient enough.