Small hard lump in armpit - been referred for urgent breast cancer screening. Looking for reassurance and advice

Hi

I’ve come on here as was referred to the urgent breast cancer screening program today and it has shaken me up a bit.  There’s the part of me that says this is normal procedure and it’s being looked at but the other part of me is anxious.

I had a mammogram end March this year which was all clear but have had a pea sized hard immovable lump under my left armpit for a few weeks.  It has actually reduced in size a bit so I wasn’t unduly worried when I saw the doctor today.  Now that she’s referred me to the urgent screening I’m feeling concerned.

I think I just need a bit of reassurance that it’s unlikely to be breast cancer due to clear mammogram end March.  Or could it be lymphoma or leukaemia.  I’ve done too much googling - sorry.  Would welcome any advice.  Thanks