My older daughter Tara was exactly like you described. I learned to distract her with TV to get her to eat a bit more. After I had my second child I realized that Tara never had asked for food, never indicated that she was hungry at all. Even as an infant, I assumed she was hungry when she fussed but looking back she really wasn't fussing for that. The first time she asked for food was a week before she turned four years old.
I had to offer her food every hour when she was a toddler. The maximum number of bites she would eat was 5 at any sitting. I was lucky if I got 7 in her. I made sure that every food group had at least one bite!! I only put about 8 bites on her plate, two from each food group. Like I said by the time she was 1 1/2 I found that if she watched TV while eating she ate better, and would eat about double the amount.
I understand how nerve wracking it is! Hugs.
Tara didn't even drink her bottle or cup well. I had to work to get her to drink more then 8 oz in a day. We put her on a "weight gain cocktail" of equal parts whole milk and heavy cream (the liquid you use to make whip cream) and a packet of carnation instant breakfast. I was under doctor's orders to give her this if she woke at night too. When she slept through the night or I gave her nothing when she woke up, she lost weight. It was either have her die or rot her teeth, I chose the teeth rotting option.
What finally made her eat though was taking milk away. I stopped the middle of the night milk by age 3. But she still wasn't sleeping through the night by the time she was 3 1/2. After trying everything I finally followed what a study the year before had said - frequent night wakings can be a hidden milk allergy. So, I took her off milk. After 5 days of no milk she was sleeping through the night and eating so much! We were shocked. By now our second daughter, Elise, had been born and was eating solids and I realized the difference in Tara and Elise in eating. Taking Tara off milk made her finally tell me she was hungry.
I'll never forget the day that Tara told me she was hungry for the first time ever. We went through Wendy's. I got the usual fries, a 5 piece nuggets and my drink. I gave Tara the fries and nuggets, she usually would eat 2 of each and be done. She finished them all and said she wanted more, she was still hungry. I went back and got another 5 piece and she ate 3 of those. This kid went from eating two nuggets to finishing 8!! It was amazing. I cried so hard. I was so happy.
What I can tell you for now is to make every bite count. Give only whole grains, fruits, veggies and good meats to him. Try dipping, some kids love that. Keep trying. He is still only 13 mos old, so you just have to keep introducing the foods to him. If it isn't better in a month ask for a referral to a pediatric evaluation for early intervention. I wish I had done that with Tara.