Net, never apologise for being worried or asking questions - we all do it and frankly I reckon this is the best pace to do ti seeing everyone here is pretty much in the same boat or has been on this same path in the past...
I am really glad you did go down the path of a biopsy as (even though it is uncomfortable now and you need to ice the boob to keep the bleeding down) you will get the right information quickly.
Also, what he said about many cancers being clearly identifiable on Xrays and ultrasounds is correct... In my case at least - I found the lump and took myself to Breast Screen who did a mammogram and then called me the next day to say they needed to do more imaging and a biopsy. The day I went back before any further work was done the Surgeon sat me down and told me mine was definitely a breast cancer as what he could see on the mammogram was very clear. And that they need more imaging and a biopsy to have a better idea what type of cancer we were dealing with. I mean, there is no way the guy would have told me "you have breast cancer" just from looking at a single mammogram (and not wait for further imaging or biopsy results) had they not been able to clearly identify it for what it is.
So if the Dr is saying he does not think it malignant there is a good chance it is just a cyst of some kind.
I will keep my fingers crossed for you and keep us posted
Hugs
Jel.