What Causes Irregular Bowel Movements?

my husband has irregular bowel movements which is not normal for him, no pain, he has lost half a stone in the last 10 days - change in bowel unpredictable, been evident for about 10 days and noticeable for about a month - have made an appointment with gp for tomorrow but would like some guidance. Loose stools, takes iron so colour not helpful, lots of wind (phew type) and very tired. has diabetes but sugars within limits, 70 years of age