Hard lump...very worried

Hello, I’m a 36 yo single mom of 2 great kids. I’m presently sitting in my local ER parking lot after being seen for a mass in my right breast which I discovered this morning. In my terror & panic, I did not want to wait. The ER has referred me to a breast surgeon who I will call tomorrow. The ER doctor agree that a hard knot can be felt but didn’t provide anything further. The lump is in the outer upper quadrant of my right breast & feels soft & movable on the surface but has a hard jellybeanshaped area that is deeper & also seems to move. I had a screening u/s 10/17 which found several cysts in both breasts. My period is due this week so maybe it is a cyst but it is not painful & I have never noticed it before. I’m very scared, as I heard breast cancer is more aggressive the younger you are; I will be 37 in September. I can’t bear to think of what will happen if it is cancer...my kids are only 7 & 9 and very much need their mother. Really trying not to get too upset as school is almost out & I want to enjoy time with the kids but I really have no one to talk to. I take good care of myself & exercise & eat well & do not smoke or drink; it just seems so unfair to have to go through this..even if it is nothing. The stress & anxiety is unreal. I have had issues with my left breast which required a diagnostic mammo but turned out fine. I had a baseline mammo 3/17, screening u/s 10/17 & my pcp did a breast exam at my physical in 3/18. Nothing was picked up on any of that besides bilateral cysts on the ultrasound. I just noticed this lump today, so not sure how long it has been there. I usually pay more attention to the left bc it causes more trouble. Could a tumor appear within 8 months?(since the u/s). Any comments or advice are appreciated, I just need someone to talk to. Going to the ER at least confirmed that I’m not losing it & that there is something there...