If you remember season 1 we saw 3 speedsters at young Barry's place - Red Speedster one from season 1 who went back to right his wrong by saving his mother. In season 1 Barry was given a choice to save his mother and live happily and he took this opportunity and went back in time. But he was stopped by his future self - Red Speedster two. This means that in the future race, Barry was forced to go back in time in order to stop the reverse flash.
Hence my theory is that when Barry ran in the past and ended up opening many portals connecting different worlds so one of them may be connected to the past too. So the zoom or the reverse flash may force him to go back in the past yet again. Hopefully in the upcoming episodes of this season!