I just installed a GFCI receptacle in my bathroom and at the same time I'm replacing an old light switch and another receptacle downline from the new GFCI. For some reason the GFCI trips when anything is plugged in the downline receptacle or if the light switch is switched on. Somehow I'm just not wiring it properly, but I'm at a loss. Attached is a photo of the array of wires in the switch/outlet combo. There are 2 neutrals, a red that is tied in with a black and two blacks split from one. Any ideas? Thanks very much.