So 14 ounces in 3 weeks is about 4 and a half ounces per week. This is on the low side of normal, the loose average is about 6 ounces. Still ok, but with a low amount of wets I think I would consult a real live LC or local La Leche Leader(<free) to see if there is something we might be missing online. Could you ask your Dr for a referral or call your WIC office?
Take a bottle and measure out 4 ounces, put it in a diaper, give it heft. Does it feel about right? Your aim is at least 4-5 of those a day according to LLL's Breast Feeding Answer Book. Page 39. At three per day you are close if the weight is similar.