4 years ago I started taking D3 5000 IU and it caused constipation, so I stopped taking it. A month ago I started taking 1000 IU for a week , then after a week I started taking 2000 IU and it again caused constipation ( this is the third week taking the 2000 IU ) . Anything I can do so I can keep taking it or I'll have to stop again ?