All I can try to reassure you with is that breast tumours are usually hard and not move able.  They also usually don't hurt. Any lump that hurts is usually not cancer. I can't imagine a tumour feeling different from one day to the next and if your doctor truly suspected cancer you would immediately be referred. I have anxiety and know it's hard but my advice would be to stop feeling it and try to forget about it for 3 weeks. It could be a cyst or another benign lump.

Jo.bs is correct. The gp would not have sent you away for 3 weeks if they thought it was breast cancer. You would have been referred. 

Also, the fact that you’re getting pain in both armpits suggests that it’s not caused by breast cancer.

Go go back and see them if it’s still there, of course. But  try to take comfort from the fact that the expert, who sees breast lumps all the time, does not think this needs to be urgently referred because they do not think you have cancer. 

Thanks for your reply! 
I'm trying to stay positive but it's really hard when there's nothing to do but think all day, Thankyou you've reassured me. 
My doctor is due to ring me next week, the three weeks is almost up but I've been finding certain things help with pain. Such as cabbage leaves (weird but it works) and hot baths. So I'm hoping for the best, I reckon my doctor might send me for a scan anyway as it's not gone away yet 

Thankyou for your reply ! 
Yeah I'm trying to keep all positives in mind my arm/ back and shoulder pain is an annoyance so I think on top of the lump I got carried away, i got a lot going for me my age which is a positive. But like I said it's really hard when you have nothing to do all day but think, I'll keep this thread updated when my doctor rings me on Monday or Tuesday. I have a feeling she'll just send me for a scan to see what it actually is, hoping for the best. Thankyou :)