The forum has had these post flush problems in the past but they have also sorted themselves out.
If you are very constipated you may need a better laxative than Epsom Salts but make sure it is OK for breast feeding.
As the pain always immediately follows eating it would indicate biliary function and it is the consensus of the group that if pain persist for several days a follow up flush may be required to clear debris that is impeding the flow of bile.
Liver pain although mostly felt on the right side can be centralised and if associated with a build up of waste in the colon refer pain elsewhere. As you are actively Liver Cleansing then the odds would dictate that pain is associated with flushing rather than anything else. It is possible that you are actually in the process of purging the problem that was causing you the original problems.
I had a awful couple of flushes one of which gave me grief for a week but I am glad now that I weathered the storm and got my self clear. This reaction is most likely going to occur one day if you have "stone" problem whether you are flushing or not. This way you have the support of the group.