Why am I not happy after treatment

I was diagnosed with breast cancer in June. Iv had surgery to remove the lump + lymph node removal. I finished radiotherapy in October and have been back to work about 5 weeks however I feel down most of the time I have no desire to really do anything. Things  I loved doing and internets before I’m not bothered about. I can’t even be bothered putting my Christmas tree up which is really not like me. I know people are looking at me thinking I’m through it all now you should be happy but then I feel guilt because I’m not. I don’t feel like my old self anymore and I don’t know why or how to move forward. Any advice would be greatly appreciated. 

Hello @Lisa scott  

I could have written the exact same post (June diagnosis, lumpectomy and SNB, radiotherapy in October), only difference is I haven’t gone back to work as yet. I’m currently signed off until January (I’m in the fortunate position that financially this is OK). I’m struggling to get excited about Christmas and facing the New Year with trepidation as I really don’t know how I feel about my job. 
Thankfully I have a 12 year old daughter full of life and enthusiasm so I’m taking my cue from her for now. 

AM xxx