Motivation is that feeling that you get when when some energetically happy song plays in the background while you're thinking of the future in a bright way, and you get all pumped up and hyped! Trust me you will feel it sooner or later one way or the other

But I do feel you completely. I am still not diagnosed but I might very possibly be ADD as well.
And I can relate so much to what you have wrote.

The technique I use when I must do something yet I don't have motivation..... - brute force.
I know you hate to hear that, but look at the bright side of it, - that's literally one of those things that will never let you down. Willpower is that last resort thing that you can always count on, even though its your most behated option
And even though you shouldn't use it often, because you don't want to exhaust yourself completely, at some certain moments for some projects/ventures that are important to you, you just must say "THAT'S FREAKING IT! I'M GOING TO GET MY LAZY *** UP! NOT THINK OF HOW MUCH IT HURTS AND HOW MUCH I HATE IT! BUT JUST FOCUS ON THE GOAL AND KEEP ON DOING IT! BECAUSE I NEED TO DO THIS! THIS IS IMPORTANT!".

Every time I did that, I felt proud after it, and although a bit spent and exhausted, several days after resting I felt even more motivated
The main thing is to never give up, cause there were points in my life where I felt sooo hopeless that any word of encouragement sounded to me like nothing, I didn't feel it, I didn't understand it, I didn't want to hear it, but these days I am much better and hopefully will be even better once I visit a psychiatrist SO NEVER GIVE UP BRO!