Whats wrong with my wiring?

I own a Squier Affinity and replaced the bridge and middle pickup with an dimarzio dp100 humbucker and dp110 middle pickup. My problem is that if the middle pickup is either connected to one of the others through the switch, or played by itself, it sounds like shit. No bass and very thin. I already checked the grounding and it seems like thats not the problem. Do you have any ideas? Thanks in advance. Cheers!