Do not worry about yield just yet. Let's ask why your plants have stopped growing. Since they have stopped growing, putting them into the flowering cycle will not achieve anything. They are not growing at all, so flowering them won't change this. I would ask if you can provide some (a lot!) more details about your set up.
Things like - what sort of lighting, what are you feeding your plants, what sort of temperatures are they in, what sort of seeds are they........ anything you think will help make a diagnosis would help the grow diary community to help you solve this mystery. After 3 months, they should e somewhat larger. There is obviously something not quite right here. Until we can sort this out and get your plants growing again, there is no point to trying to make them flower, just yet. To say I am intrigued would be an understatement. Lets see if we can get things back on track for you. Hope this helps.... Organoman.