Although you have had some of these symptoms since before you were pregnant, pregnancy can't be the main cause; but the hormones associated with pregnancy may be intensifying the situation.  A color change in the nipple is common during pregnancy, too.  Pain is not usually a breast cancer symptom, but it can be one early symptom of a rare type of breast cancer called inflammatory breast cancer (IBC).  Usually IBC advances rapidly, so if you had it, you would probably also be seeing swelling, skin dimpling, and other symptoms.  Of course, the IBC symptoms overlap with pregnancy breast changes, and you would expect to see pregnancy-induced changes on both sides.  

Since this is just on the right side, you might also consider whether you are straining the muscles under the breast (maybe lifting one of your other children?).  I think a little concern, but no panic, would be about right.  Be sure to let your prenatal care provider know what's happening.  Talk over changes in your physical routines, personal care products, and so forth with him or her to brainstorm some more about possible causes.  If your symptoms get worse, don't hesitate to ask for a referral to a breast specialist.  And don't worry about the baby; tests and treatments for breast cancer can be planned so as not to harm him or her.  I think everything will check out fine, but you'll be able to enjoy your pregnancy more if you know what's causing this pain.