If you are using CC 2015 the normal behavior for starting a ram preview is as follows.
Press the space bar or the preview button once - the ram preview starts
Press the space bar a second time - the ram preview starts to loop all frames that have been rendered
Press the space bar a third time - the ram preview stops.
If you wait for a ram preview to fully render then the second time you press the space bar or the start button the preview stops.
If you press the start button or the space bar a second time before AE has cached all of the frames then AE will only playback the rendered frames. Do this quickly and you could easily end up with a looping preview that is only a few frames or even a single frame long. Try waiting for the ram preview to complete.
The other possibility is that you have your work area set to just a few frames and the ram preview is looping the work area.
If this does not solve your problem then we need to know your OS and system details and your version of AE down to the last decimal point. We also need a detailed description of the workflow that leads to this error. If you are new to AE please start here to learn how it works: Basic Workflow
ok, what you said about waiting for the clips in ram or something worked, but sometimes it gets to 1 certain clip then plays in real time automatically. is that normal?
also, do i have to wait for the ram preview to fully render or can i just add it to the render queue and w8 for it render properly, then play it in the file it exported as?
You don't have to do a preview before you render it out of the render queue.