Whimsy, please go. I would bet that you are fine and there is nothing sinister underlying the feelings you have - I think you are just reacting to the scare that you had when you found the lump. If you had had the mammogram / ultrasound and been given the all clear, then you probably wouldn't be feeling like this now, but because you only had a physical, a part of you isn't 100% sure that everything is okay and I would bet thats why you are feeling this way. Also, some women who do have cancerous lumps in their breast, want the breast removing, not just because of the cancer, but they feel its not part of their body anymore.
That said, not all cancers of the breast start with a lump - my friend, for example, had breast cancer which was detected when she had a vague but persistent tenderness in her armpit.
So, I would see your GP for a referral and ask for a mammogram / ultrasound - if there is something there, it will be detected; if there isn't, I think the procedure will set your mind at rest once and for all and get rid of the feeling you have
Honestly, your GP will trust your feeling that all does not seem well, he won't think you are being silly or hysterical. Please go