I can't offer any medical advice (obviously, it would be completely inappropriate). However, if you are not happy with your treatment/diagnosis, do NOT let it go. Arrange to see your GP again (or other doctor at your surgery - a female dr, might be more open to your concerns) or the consultant at the clinic and take a long a friend / family member for support. Yes, you are young, but I think the whole point of these forums, and the gazillion facebook memes of oranges, is that cancer can happen to anyone, at any age. You clearly have discomfort, and it is worrying you, and I doubt you will be happy until you know the underlying cause - so go back, with someone who will fight your corner / stand up for you. Oh, and if the lack of 'bedside manner' happened whilst at your local / hospital Breast Clinic, ask for a Macmillan / Breast Care nurse to be present too. Also, get them to explain what they saw on the ultrasound that makes them think it's normal breast tissue, and what else could be happening to explain the pain - ask if you should have further tests... don't let them 'side line you' just because you're 22.
I hope it all turns out to be something simple / minor, but if it doesn't, you'll be glad you went back and pushed for your symptons to be properly considered / diagnosed sooner.