Baby blues?

So my baby boy is now 3 months old. (Time flys!) when he was just weeks old I found  myself really sad and sensitive but quickly got over it. Now fast forward 3 months later I'm getting that "sad" feeling again. I find myself laying my baby down to sleep for the night hoping I did enough for him and hoping he had a good day. Sometimes I just wonder if I'm doing a good job or if my baby is happy with me. It makes me Sad not knowing if I'm doing a good enough job as his mom. I want nothing but the best for him and I just hope I'm doing a good job.
On top of that, I'm going back to work soon and the thought of that puts an ugly feeling in my stomach! I can't help but to cry. Is anyone else feeling like this? Not sure if this is baby blues again or am I just being extra emotional or is this normal feeling to have. Anyone else? Or am I alone? lol