I wouldn't be concerned about not seeing fusing going on at 2 months. For most people, it doesn't even start to be seen on x-ray until at least 3 months. For many people, it takes even longer. Just keep doing what you're doing, walking, using the bone growth stim, etc.
If you have to pick up kids at the day care center, you probably aren't going to be back at 4 months. It must be frustrating that he keeps giving you different answers, but I guess it's hard to predict. Everyone is so different.
At least you're having less pain. That must have been terrible, dealing with the headaches and flu while you're recovering from such major surgery! I wish your doctor had told you that it's very normal to still be having pain at this point. It is, you know! When I had post-op appts and told my doctor I still needed pain meds, he would just give me a sweet smile and say, that's okay, you're still early on in this. (Can you tell I loved my doctor?) I found that 3 months was my first big turning point. I started feeling more human again, was able to cut back on the pain meds, and was able to be out of bed more than in it. 6 months was the next big turning point. It's a long recovery, but you'll get through it. Hang in there! It WILL get better!
I wish you the best! Don't lose hope!