Yes, you can do it sooner, but is best to wait the two to four week interval. That allows the bile to build back up and have the force to push out the stones.
My first flush I repeated in about 8 days because I was very uncomfortable. I got out quite a few on my 2nd flush anyway.
If you are truly uncomfortable, go ahead and do it. I had that shoulder pain, etc for 6-8 flushes before I felt significant relief of symptoms. Just remember to eat correctly, good oils, lots of water, bowel cleanse, and maybe consider a parasite
cleanse in the meantime.