HiHeather,
My son is 14 months old, and is still nursing. He is down to probably 3 times a day, usually when he is tired. My daughter nursed until about a year and a half old.
I started my son on cereal at 5 months old, only because his dad (this is his first child) was so anxious to start. He wanted to start at 4 months. He came home from the store one day with a box of mixed cereal, and was like, "Let's feed him!" I compromised with him for 5 months old, and baught a box of rice to start with. hehe.
Anyway, at my son's 10 week check, he weighed 16 lbs. he was perfectly fine with just nursing. He now weighs 20 lbs 14 ozs. He eats all the time, but just has a really high metabolism (like his daddy. I wish I had that problem!)
I am sorry that you are regreting your decision to start solids. I would say that your son doesn't really need them, and that you don't have to keep introducing more. Let him eat what he has had, and let that be sufficient. I am not a doctor, and I would suggest speaking with another doctor to get a second opinion. I haven't heard many doctors push baby food on infants so young. The ones who do, I have found tend to be uncomfortable with the idea of nursing to begin with. Not that I am saying your doctor is anti nursing or anything, just get another opinion. And go with your instincts.
My sister nursed both her kids for about three months, then switched to formula and cereal. She was staying with me when the baby was little, and kept telling me around the three month mark that I had to switch to formula and cereal, because William eats constantly and is starving to death. Then I brought him to the doc and he was 16 lbs and perfectly fine! I had told her to mind her own because I was doing what I felt was right for my child, just as she had for hers. I am glad I made that decision. Anyway, talk to another doctor. My opinion is not to keep pushing foods on the baby. Breast Milk is enough. Just make sure you are taking your vitamins and eating well.
Liz