Hi... it's a horrible place to be... no you have just had surgery so you shouldn't be feeling 100%, that's not realistic... you have gone through a huge life changing experience which will take a while to digest. You don't need permission to cry .. and yes, you are absolutely normal.
Can I suggest a couple of things... ring a friend/close family member for a chat, tell them how you feel (trust me, sharing really helps), and when it's daylight... go for a little walk. You will be amazed at how a little exercise helps.
Check out this web site... read other peoples blogs and connect with people who have been there.. done that. You will get through it, it just takes time. If you haven't already done so yet - order the My Journey Kit from this site and if you are still feeling down ring the doctor...GP, Surgeon...
I'm not sure where you are at, at the moment... I'm assuming you have just had surgery and are maybe waiting for your pathology results... and I cannot offer any medical advice... what I can tell you is that whatever is ahead is 'doable'... and you'll get through it... you will even function and be able to look after and play with your children. Chemo is difficult but looking back (I finished in September last year) not too bad, and Radiation was a walk in the park...
take care and know that there is someone in 'cyber space' sending you a big hug, thinking of you and wishing you the best.
Trina