I Have Been Taking Lenzess For IBS With Constipation, For

I have been taking Lenzess for IBS with constipation, for two weeks now! I only use the bathroom once....about 30 mins after I take it, the the urge to go doesn't come back until I take it again!! Is this normal?
Also my doctor put me on metformin 500 last week, my a1c was 6.4!
One of the main side effects of it is diareah!! I have very lose stool....but only once a day!!
One of the two meds are making me extremely sleepy!! Which one could it be? Neither shows that as a side effect!