Hello,
I don't think you would be a bad mother if you leave your baby at 7 weeks to go back work but, try to find another option. I mean,to tell the truth, your child is still young and he or she needs you more and more and he/she will never find someone who will take car of him/her better than you. Me for exemple, I decided to open my dayhome and don't leave my son untill he is unless 12 months;like this I earn money and I have my son with me. But if the baby stay with your husband or a member of your family I think it's easier. So, in the end,it's your baby and your decision and you better your situation than us.
I hope it's help you a bit.
Good luck
sihem