wafer cutting into stoma

i have had my colostomy for 5 days.  i have changed the wafer 3 times.  i cut it to fit but when i change my bag the next day, the stoma seems to have grown or the wafer shrinks. the part of the wafer that you cut turns white. is that normal?  i just changed my bag and i now have what looks like cut marks on my stoma which is probly why it was hurting bad.  has anyone else had this problem? i cut the new wafer alittle bigger this time so i will see what it looks like in the morning.  and how do you know when you're constipated?  i havent had output for almost 3 days.  should these be things i should call the doc about or are these things normal?