Might I suggest a variation when it comes to the bridges? Take a Swiss ball and either a box or a bench, lock elbows on the ball and place feet on the bench/box and hold for at least 1 min for 3 sets, if you still do not feel anything the you can hold this no problem for up to 1 min 30 bump it up one more time. Take a 4 kilo medicine all (at least 10" in diameter) and place your feet on the swiss ball and your hands on the med ball and hold. When this become easy you are ready for a one legged version of the prone bridge. You can switch to a one legged prone bridge right now and hold each side for a min of 45 secs. Just because you do not feel the burn one way does not mean you will not feel it another way. I know all these are just prone bridges, but all of my ideas work the core the same way. Try the swiss ball and med ball, if you can hold that solid for 1 min 45 for at least two sets then you are making gains. A small variation to some of the lesser exercises is okay. IE... Push ups, pulls ups, prone bridges, revers crunches.
Let me know how they feel, Christian


