What have I done/What can I do?

My son (8weeks) was sleeping from 11pm to about 5.30am until he had his 6 week injections. Now he wants to have his 'big' sleep from his late afternoon feed (finished anytime from 4-5.30) and we have to wake him at about 10 to feed him so therefore he is back to waking about 3am.
We woke him up the last two nights about 7/8 for another feed in the hope that having the extra feed before midnight would mean he would sleep through again but he still woke up 2.30/3. He wouldn't take his whole feed at either time we woke him AND then this morning he chugged his milk so fast he vomited it back up and then wanted more I should mention that 2 weeks ago he was waking himself at this time for a feed but dropped this one (7/8pm) after his jabs.
I know that babies start sleeping through when they are ready and don't really want to force it (just wondered if he wasn't sleeping through because we let him sleep so long earlier )
I guess what I'm wondering is, is it Ok for him to be having such a long evening sleep (5+hours)? Will he start sleeping a little longer after his last feeding 10/1030pm? (he's only sleeping 4 hours approx.) Should I keep trying to force an extra feed on him? (am reluctant to do this though)

I agree with busymum in the fact let him do his sleeping when he wants as at 8 weeks his routine will change again with the growth spurt. Rhyley was sleeping thru at 7 weeks ( till 7 in the morning) but along came the 3 month (more like 3 and half for us) growth spurt and it all turned to custard, he made his bed time himself which is in between 7 and 8pm but he'd wake more often in the night, he only wanted to be fed in the middle of the night like 3am which only lasted a couple of weeks but the waking at 3am lasted.
So after all that mouthful I would wait till he woke up and then feed him, I know some ppl dream feed which you can try but until he sets a pattern that would be hard to know if hes hungry or not. Mind you correct me ppl if I am wrong as I never dream fed.