Breast lump appointment TOMORROW

Hi all! I've been a long time reader of this forum but have never posted but now I could really use some advise ? 
So...I'm 27 & I found a lump on my left breast 3 months after my mum finished her treatment for BC (Awful timing, Right?) 

I obviously booked an app with my GP for the next day who examined Linda the Lump and has referred to me the breast clinic mainly because of my mums recent diagnosis . Now I understand we are in a shakey time rn but the clinic called with no appointments available for at least 12 weeks so I've been in the spin of the unknown for a while now, my mood is low, my self confidence is gone I don't  ever take my top off anymore & my boobs haven't even changed but the unknown does this to you, you look at your boobs as if they're murderers !!

My wonderful husband has booked me into the Nuffield private clinic tomorrow morning who've said they will give me a consultation & then an ultrasound or mammogram same day and I'm so nervous even tho my own Gp did say it "felt" like a cyst I'm starting to get what feels like an ache in my upper arm as if I've been exercising ( I have not haha)  the lump seems to get bigger at "That time of the month" too . Any advice? Words of wisdom? Or maybe just a woman who's been through this ? 
Thankyou! Hope everyone is staying safe

Antonia x