I have questions regarding my 2000 Dodge Durango?

There are a few things that have started happening recently on my 2000 Dodge Durango. First thing I noticed was that even when I am sitting in park the engine will rev. It does it all the time now sometimed reving to 4 or 5,000 rpms. Then the check gauges light came on and I noticed the oil pressure gauge was down to 0. It does this often. It will drop and then come right back up. Now yesterday I notices a slight ticking sound. What is going on and what should I do? Money is tight for me right now and I am not sure if I can afford a mechanic.