Help! 4.5 months and not eating much!

Bee

My LO is 4.5 months old and is not eating a lot even with all the milk I am producing. I'm a bit worried because at our last ped appt, his doc said he was a bit behind on his weight scale. He was 8lbs 3oz at birth and now weighs 13lbs 13oz. He was a great eater before but now he just wants to sleep, play with the bottle, or nurse for a few minutes....He doesn't eat more than 5oz of breastmilk in a bottle, and won't nurse longer than 3-5mins during the day and about 10mins in the wee hours... He eats every 4 hrs... When he breastfeeds, I'm not quite sure how many ounces he's actually eating...Plus...he's so curious about everything around him. He gets distracted by any and everything so he pulls off he nipple or bottle so easily... The ped wants to see him again in 3 weeks to make sure he's not losing weight or not growing fast enough... Anyone in a similar boat as me? How do you get your LO to eat more? I would like to continue giving him breast milk but if his weight doesn't pick up, we may have to start him on solids.