Is the part that is retracting the nipple head itself? Does it "come out" if stimulate it or if it's cold? This can be normal and could just be how your breast are forming. Same with your lump. I naturally have lumpy breasts and some of the tissue is actually pointing outwards. The ultrasound technician told me well it's healthy and normal tissue, your just lopsided. Each breast is different and that isn't necessarily a bad thing. If you're doctor isn't worried, you shouldn't be.
It's very good that you're watching your breasts for changes though, because not all breast cancer comes in lumps. There is a form of breast cancer that shows itself by an "inverted" or "dimpled" nipple as well as possible bleeding, crusting over, or leaking nipples. However in these cases I believe the nipple started out very normal and then just suddenly changes. (I also believe these are among the more rare cases of breast cancer, but I'm unsure of their numbers, so don't quote me).
Also if you're curious about naturally inverted or flat nipples vs cancerous once, have a look through Google images. It might give you a better idea of healthy vs unhealthy breasts.
Yes, it's the nipple head. It does come out on it's own when cold. The lump itself doesn't concern me, but I don't think my nipples were like this before.
I'm going to talk to my Mum about it and see what she says.
So this could just be natural for me as my breast grow?
YES, some women naturally do have inverted nipples and it's not all that rare. That's why I said if the doctor isn't worried, I wouldn't be. It is a good thing to keep watching because some breast cancer manifests itself that way, but your doctor should have looked for those other signs. Also asking your mom about it is probably a good idea. I think it's possible to have inverted nipples since birth. If you are uncomfortable or self conscious with how they look, there are specific cosmetic surgery to make them look more "perky".