1999 Dodge Caravan Won't shift out of first gear

For the past few months when I would first take off the van would seem to bog down or kick a little but then go ahead and resume speed and be fine. It might do that two or three times a week or not at all for two weeks. It was very sporatic. But a few days again it did it again worse than it ever had and my speedometer seemed to go crazy during the bogging down or it would not owrk at all for a little while. The van would eventually go after it seemed to get out of the bogging down and kicking thing. Now it will not shift out of first gear it seems no matter what the rPM's are. This is my only vehicle and I have 5 children. Can you please help me to find out what is wrong?