I would call your dr and your OB. Good luck Breast pains are normal. Often times you are told to wait because your body needs time to heal and rid itself of the toxins used to treat cancer. These toxins can be harmful to a fetus and cause birth defects and miscarriage. It is dependent on which type of medications were used so I cannot speak to your personal situation just in general
They might have said that to make sure all the medications were out of your system and you would be strong enough to carry the pregnancy which does take a toll on your body. That might be why. but wait until you see your doctor to see what they say. everything happens for a reason. good luck and keep posting so we know whats going on