A strange BB hand

5 handed, very first hand at the table so no reads

Preflop MP limps, SB limps, i check A [img]/images/graemlins/club.gif[/img] 5 [img]/images/graemlins/club.gif[/img] in the BB.

Flop A [img]/images/graemlins/diamond.gif[/img] 7 [img]/images/graemlins/spade.gif[/img] 8 [img]/images/graemlins/club.gif[/img]

sb checks, I bet, MP calls, sb calls

Turn 6 [img]/images/graemlins/spade.gif[/img]
sb checks, i bet, MP raises, sb folds, i call

River 5 [img]/images/graemlins/spade.gif[/img]

I bet, Mp raises, i call

is more hand strong enough to raise preflop? and is the river just a check call?