1997 Toyota Pickup white smoke from tail pipe and foam in r

I make white smoke coming from my tail pipe after about 10-20 seconds after I started 2 weeks ago. So I changed the motor oil. The next day the smoke was gone. Two days later I drove To school, where ia about 10 miles away. When I got there I noticed that the water temp. gauge was higher than normal. The next day I checked the radiator and there was no coolant. I put in Prestone 50/50. I drove the truck to work the next day which is about 50 miles away. When I got to work the truck started to vibrate a little and then the check engine light come on. I truned off the car and went to work. At lunch I looked in the radiator, and there was weird colored foam coming from inside the radiator. I then started the car and the white smoke returned. I disconnected tyhe battery to see if the check engine light would stay off, it did. But, since I live so far, I called a tow truck. After my truck was removed from the tow, I started my truck, and to my amazement, the shaking was gone and the truck felt fine. So I test drove it, and it felt fine. Is it? Or what is the problem?