In my experience Calculus was a tough nut to crack. This was mainly because it is usually taught in a way that forces you to chew lots of preliminary materials which seem completely unmotivated.
But obviously, Calculus was not developed the way it is taught. I found historial approaches more motivating. That means either using infinitesimals (17th century approach), or starting from construction of the real number, say Dedekind cuts or Cauchy sequences (19th century approach).
If you're having trouble then I'd suggest that you pick up Calculus Made Easy by Silvanus P. Thompson. Best book I've read on the subject by a country mile.
But obviously, Calculus was not developed the way it is taught. I found historial approaches more motivating. That means either using infinitesimals (17th century approach), or starting from construction of the real number, say Dedekind cuts or Cauchy sequences (19th century approach).