no differnce in the execution time between seq. and parallel programs

Hi all
please can any one help me to find the reason??

i am using LLVM to execute two programs both of them was exactly similar but the difference was the first one is a sequential program has three functions. In the second program i am trying to execute it by giving each function to thread (three thread work in parallel way) ,but when i am trying to calculate the execution time i found the execution time for parallel one larger than sequential one ???

note
I execute both of these program in gcc compiler and i found there is a difference in the execution time between these programs.The parallel one was faster than the sequential one.

i will be thankful if any one can help me
Regards
esraa