I agree with PowerIso. It seems harder because you cover a lot different topics. You go from integrating with the power rule and simple substitution in Calc I, to integrating exponential functions, inverse and hyperbolic trig functions, integration by parts, and trig substitution. You do volumes of revolution, improper integrals, and l'hopital's rule. You study series and sums and all the different tests for convergence and divergence, and McLaurin and Taylor polynomials.
For me, it wasn't that the material was more difficult (it is, slightly, but not much), it was that it seemed like that semester of calculus would never end. Just grit your teeth and work through and you'll be fine. Before you know it, you'll be on to Calc III and ODE, and that's where the fun begins.