What Causes Severe Tiredness After Taking Omeprazole For GERD?

I have been on Omeprazole for six days for GERD and esophogitist. Since taking the medication I find that I am very tired and can't seem to get enough sleep...is this a side effect? Before taking this medication, I had difficulty sleeping and would wake after 4 hours. It just seems very odd. I also take Synthorid .075 for hypothyroidism. Can the Ompprazole be affecting the absorption of Synthroid?Thanks!Shirley