Hi I've got two big lumps under my nipples and they are very tender. I'm very embarrassed about them and I'm worried I could have cancer! Please can someone tell me what thic could be

Without a proper exam no one on the interenet can tell you what YOUR lumps are. Yes cancer is one option, among other options.

The only way you will know, and you need to go in case it is something serious, is go to your doctor for an exam

It's hormones. I have known friends of mine that had that growing up. They had the same thing. It goes away once your body settles down.