zipper

how do you play small pairs at a full table,i consider small pairs js or less,,limping in early i always get raised, raise early and i always get 5 callers
i also always feel beat once the flop comes ,,isnt there always overcards..
the other day,100/200 blind 40 person tourny. im on the small with a/k, first position bets 500 ,every bodyfolds to me , i go all in ,,1900 , big blind calls , first position goes all in..big blind calls 2600 ,,we all flip over ,,,first position has 77
i cant believe he called,, is this right, big blind has a/j,,i had been watching 1st position and he was loose , big blind had just took a big hit so i was on gut feel ,,why would he call with 2 all ins in front of him,,,he has to know we have over cards ,,i would have folded, is this right..flop is j,7,whatever,i didnt mind the beat by the j but that 7 just hurt ,,was he just reckless or does he know the secret to small pairs ,,it just got me more confused...zip