Receiving end problem in BPSK modulation

I have been trying to design a BPSK modulation and demodulation scheme
using GNU radio. Until now I have been able to design the transmitter part
of the BPSK modulation. But right now I am stuck at the receiver part of
the BPSK. Though I am receiving data, I'm facing a few problems which are
as follows:-
1) The packet length is changing continuously from the out_pay of the
header payload demux.
2) The data which I'm receiving is coming after a few seconds. How can I
solve this delay problem?
2) Whenever I am trying to get the BER or using any kind of comparison
block the output of the flowgraph starts freezing.
I think maybe I am missing a few blocks but I have searched a lot but I
didn't get any definite solution for this problem. I would be extremely
grateful if anyone can help me out in this regard.Thanking you in advance.
Regards.
Sujay Mondal.