I personally couldn't handle khan academy because of the stuttering..it became extremely annoying and distracting...i've recently discovered cramster.com (it's 10 bucks for 4 weeks, there's an annual rate too but i'm not sure what it is) and it solves all the problems in a bunch of different texts with explanations. this is how i'm teaching myself physics.
for chemistry, I searched topics in youtube till i found a professor i liked.
for physics, i highly recommend username vkiledj (if you'll be needing that anytime soon)
good luck! just keep doing problems, it will click 🙂