I have two 12" JBL subs and a 1800watt Pyle amp and I need help?

The other day I had both of these JBL-GT1241D 12" Woofer hooked up to the PLA2210 1800W 2-Channel Chopper Amp and they sounded GREAT! but now i am having problems. When I hook them up now the sound crappy the have no b unless I bridge one of them. What am i doing wrong now?