Villain is a half-stack fish. Been limp/calling a ton pre. He could very well have a set, two pair or Qx. Doubt he'd do this with a draw as he hasn't been very aggro.

$0.25/$0.50 No Limit Holdem
CakePoker
8 Players
Hand Conversion Powered by weaktight.com

Stacks:
UTG ($10)
UTG+1 ($25.65)
MP1 ($25.03)
MP2 ($98.80)
CO ($50)
BTN ($6.75)
Hero ($49.25)
BB ($98.05)

Pre-Flop: ($0.75, 8 players) Hero is SB
2 folds, MP1 calls $0.50, 3 folds, Hero raises to $2.50, 1 fold, MP1 calls $2

Flop: ($5.50, 2 players)
Hero bets $3.50, MP1 raises to $7, Hero?