Constant pain in left breast. Or normal?

I have constant pain in left breast,it mostly pain at the sides of the left breast.i have constipation problem too.my left breast is bigger,fuller and painful than the right one! The pain comes and goes by time.i use to wear undersized bra before!is it pains because of this or something else??yesterday i have noticed a lump in my left breast which is small but the right breast is also having a lump!both the breast is having lump on same side! I'm worried is it a cancer or something??i also get breast pain before periods! I'm about to expect periods this week,please let me know soon that this pain is harmful or normal??few months ago i got this pain and I consulted the gynaecologist she said it's normal but now this pain has come !what to do let me know please..