You are right, there is something occuring within your relationship.
There are other considerations here.
For instance, are you calling him a great deal (is it more than once a day when there are actually no plans occuring?). Perhaps there was too much communication, or at least, telling and he has to listen. I don't really know if that is occuring or not, but it could be a possibility.
Maybe he feels that the relationship is going so well that he doesn't need to respond to each and every request as he feels there is a deep rapport with you.
Maybe he just isn't that into you anymore. He might just be avoiding you, not even seeing anyone else because he isn't into you.
Probably the last one is more likely. Some guys would rather avoid a confrontation (which is inevitable) so they don't have to see how they make women cry.
So yes, there is "something going on" but you won't know what it is, until you ask him and are ready to listen.