<p>The first language I learnt  was PHP, but I have more recently picked up Python. As these are all 'high-level' languages, I have found them a bit difficult to pick up. I also tried to learn Objective-C but I gave up.</p>

<p>So, what language should I learn to bridge between Python to C</p>

It's not clear why you need a bridge language. Why don't you start working with C directly? C is a very simple language itself. I think that hardest part for C learner is pointers and everything else related to memory management. Also C lang is oriented on structured programming, so you will need to learn how to implement data structures and algorithms without OOP goodness. Actually, your question is pretty hard, usually people go from low level langs to high level and I can understand frustration of those who goes in other direction.