Is it normal to have breakthrough bleeding whhen channging the pill?

i have just changed my pill after 2 years on Levlen ED to Norimin as i was havinting with my first pill, now 2 weeks into the change i am having breakthrough bleeding, heavier than before? is this normal? i have an appointment with my doctor in a month should i go earlyier, or wait for the bleeding to stop?? and how long into the cycle does the bleeding usually last?>? thanks