Could the morning after pill (levonelle) be causing breast tenderness 8 weeks after taking it. negative pregnancy test and 3 irregular periods since?

No: The levonelle is out of your system at this point but your own hormones can cause breast tenderness. If you are having irregular periods that is a sign that your hormones are out of balance and it would be a good idea to see someone to find out why. If also could be due to a more reliable method of contraception that you are hopefully using now. Hope this is helpful. Best wishes