Mandy I know where you are coming from! My son is 5.5 months old and weighs 21 lbs! He is a big eater!People always have there comments on feeding baby solid food before 6 months..You know yoru child better then anyone! So don't ever listen to what anyone says! People always comment on how large my child is..it hurts! . He is thriving!! Don't ever let anyone tell you not to feed your baby solids!! And if he is hungry..feed him!! My son was also gaining a pound a week until I introduced solids and now he has stabilized and is gaining the 1-2 pounds a month!Afterall Tracy says in her book under 'Solids before 6 months' a baby names 'Jack..i think' was 20lbs at nearly 5 months and she said in thsoe circumstances you can feed them solids. that is definatly our babies!!
As for the original post, I think he is snacking! my son was the same way..then at about 6 weeks we got on the EASY routine and it's been golden ever since! Eevry now and then yes they will be hungrier and you will need to feed them more..but having a routine will make your baby alot happier!