Returning back to work . UUGGHHHH

I'm returning back to work this week and I have been sad and crying for the past few days. I have been with my baby since he had been born and he is almost 12 weeks. This is the first time I have stayed home with one of my children before. This will also be the first time that I will be putting a complete stranger with one of children when they have been this small. I'm sure I will jump back into routine. After all, people drop there babies off 4-6weeks of age with no problem. Any advice on how to make it easier and on both me and him? I miss him already and he's not even gone yet. It's gonna be the longest 7.5 away from him ever.