Advice on changing milk please??

[fifisworld]

Could anyone give me advice on something?
DS2 is almost 6 weeks and is doing really well with his feeds etc, he has 5oz of milk every 4 hours or so, but during the past couple of days he's wanting it every 3 hours, but then he's being sick which i think is because he's having too much too soon.
Ive tried giving him less but he cries for more.

So i bought some hungry baby milk which can be used from birth, do you think if i alternate him between this and the normal milk it might help him go longer, coz he would stay full for a bit longer or would this upset his tummy?

Thanks SWC - Funnily enough, ds1 was on hungry baby milk from being a couple of weeks old and he's always been constipated, even now he has problems and he's almost 2.

Not really projectile, but more than just the usual sick that comes up after winding him and its not after every feed either.
Sometimes he wont take the full 5oz which is fine but then he's hungry again a couple of hours later. So when i do feed him again he drinks it but is then sick which makes me think he's had too much.