Many women with Fibrocystic changes,develop cysts and Fibroadenoma.These benign lumps will generally increase in size before the menstrual period and decrease afterward.
Avoiding foods and beverages containing caffeine, such as coffee, tea, chocolate and soft drinks, can decrease water retention and may help to alleviate the discomfort and sometime even shrink the cysts.
As I mentioned in my previous comment,it is best to have this lump "that feels more distinct" further investigated just to make sure.
Talk to your doctor about your concern regarding this particular lump and see what he/she suggests okay?.
I forgot to say my doctor told me I also had lumps in my other breast but this one feels more distinct I had a ultrasound 2 years before on both my breast but I can't remember if it was the same lump or not..
Not all palpable lumps will appear on Ultrasound or Mammogram.Each test has it's limitations and what it can pick up.Since you are worried about this lump,I would suggest to get the opinion of a breast Specialist,because when a lump is palpable and doesn't go away,it is usually recommended that the lump be biopsied to determine what it is exactly.
A fine needle aspiration(FNA) is a simple procedure.Fluid will come out if it's a cyst .If not, tissue in the needle can be examined under the microscope for a definite diagnosis.
It is probably nothing to worry about (as your Doctor suggested) but you have to make absolutely sure that the lump is harmless.