It means that Ponyboy feels that things are happening at a pace that is quick enough where everything feels out of his control. He doesn't have time to mentally and emotionally process all that is happening and has happened before something new comes along to deal with.
Yes, I get that feeling every once in a while. For example, right now that's about how I feel. I teach high school, and school starts in 2 days. I found out this morning that a class I had worked on all summer is not being offered any more this year. Instead I have to teach a class that I haven't taught in over a decade starting tomorrow. On top of that, I was asked to take over the cross country team 3 weeks ago. I'm fortunate and grateful for my job and the confidence being placed upon me, but things are happening very fast right now. I know what Pony is talking about.