You have too many irons in the fire. It's time to scale back your commitment, even at the risk of alienating colleagues. It simply isn't realistic for you to perform the work of three people. Until your boss hires more staff, the problem will get worse. It may be better to seek a better job than turn a blind eye to the problem. Are you unemployed? If you're going to find a position, you must decide what kind of work you want to perform.