how do you feel when you calculate the price for a customer? do you feel as though you're charging far less than your work is worth? do you set your prices out of fear of rejection? or, do you know the price is fair exchange for the value of your work? if you know the prices are significantly lower than the going rate in your area, do you feel good about that, knowing you're a resource for less affluent quilters? when you answer these questions for yourself, you'll know whether or not you should raise your prices.
either way, you should definitely give yourself a reasonable amount of time to get to, and complete, each commission. you aren't being fair to yourself or to your customer if you promise to have it sooner than you can actually get it done. (in addition to the quilts-in-the-que, you also need food, sleep, and occassional interaction with other human beings. don't push yourself to exhaustion.) just let each new customer know they are in line and then give a realistic estimate of the wait for theirs to be done. if the customer doesn't want to wait, encourage her to go elsewhere. make a referral to another quilter you trust. the customer will appreciate your honesty and either come back next time or at least spread good words about you.