Set to 12 psi at 37-38f for two weeks. Beer was flat. Set to 20 psi for 3 days, then back to 12 psi. Now I get 3/4 glass of foam an 1/4 beer yet the beer is still flat tasting. Do I just leave at 12psi and hope it straightens out. Is it common to get that much foam and have beer still be flat?