Brown discharge is normal after your period even if its just once in awhile. Its old blood and your system is just cleaning its self out. I don't think you're pregnant yet but keep trying and try to keep your stress down. I'm sure it will happen.
Sounds normal ...I've had that happen on random occasions too. As long as it stops you are fine
Have you taken a pregnancy test? A females cycle can be off and different for a number of reasons beyond pregnancy, but until you've had a test done it's hard to make guesses.