Feedback is an ever-present problem when amplifying any instrument. Feedback is a still bigger problem when amplifying an acoustic instrument because of the fact that the resonant qualities of its body make it more likely to be stimulated by the sound from the speaker. When the instrument is stimulated in this way, the pickup then retransmits this signal to the amp. The cycle of retransmission causes feedback.
We recommend, when playing at louder volumes, you make sure that your instrument is as far as it can be from the speakers that are projecting your signal. Sometimes, simply turning your instrument away from the speaker while playing helps to eliminate feedback. Another recommendation would be to use a headphone monitor so that you will be able to have the speaker far away from you and still have the ability to monitor yourself. Another technique is to wedge high-density foam (a Nerf football) between the tailpiece and top and into the f-holes to limit extra-sonic vibrations.