Help! Can't access 1st gear- others are hard and they slip

Hey guys, I'm new to forums but a friend suggested it may help. I have a 1989 klr650, and today I had been riding in pretty hot weather and I'm not sure where my oil went but it was almost empty. I regularly check it, must only have been 4 or 5 days at most since I saw it was fine. However today about an hour into the ride I lose the ability to shift into first gear, I push down and it just comes back up. (this caused me to stop and look at my oil level) As I try to get to the nearest gas station to get oil it starts to get harder to shift between gears, same problem it won't catch I guess it a good way to describe it. Upshifting hasn't been a problem but downshifting is where the trouble is. Then I fill it with oil and let it cool down (a small amount of white vapors were escaping the oil filling hole). Riding back the problems remained and it would change gears on me, and only once did I hear a grinding. What should I do guys? This is all I have- no car :(