It sounds like sleep apnea to me. Does she stop breathing, and then suddenly gasps for air because she's oxygen deprived? Your doctor is right, that baby's breathing can be irregular in infancy, but you might also want to research apnea.
http://www.**********.com/0_sleep-apnea-in-babies_1741484.bc
Oops, sorry, apparently that link isn't allowed. Just google "sleep apnea in babies" and you'll get information.
i just read a few articles about the sleep apnea that made me more nervous... Today i took my lo to the dr office because she had trouble breathing like even when she cried it was difficult for her to make a sound an her cough was croupy her dr took her in right away and said she has bronchiolitis and prescribed her some abuterol and another medicine i think shes doing a bit better than this m9rning...