The Jays looked really good at the start of the season, but as they tend to do down the stretch is get tired, namely, with their pitching. Despite having the bats, they simply do not have a confident rotation and no clear cut ace. Look at the roster and a lot to do with it has to do with age or lack of production.
R.A. Dickey is a knuckleballer that is getting long in the tooth, and his individual record speaks for itself. Mark Buehrle is in the same boat and losing control of his once money fastball that he had when he was with the White Sox. Don't even get me started on Happ. Drebek is also shaky and is reluctantly going to be moved to the bullpen - the first time in any league that he's been in.
The other problem is that there are teams in the AL that are just stacked with pitching (Detroit, Oakland) and it doesn't help that you are in the East with a lot of teams that just chip away at wins, as opposed to the mediocre Central.
Get the pitching straightened out, and the wins will come (as long as they can hold onto Bautista, Encarnacion, Cabrera and company).