I am 12 weeks pregnant and constantly worried about miscarriage - I always have slight bleeding and after visiting my doctor twice in this regard, I have confirmed that this is not from Vagina, but it is due to constipation. I have no stomach ache or severe cramping as I get to read / hear about miscarriages. I am otherwise normal and dont even have morning sickness (sickness only at evening after 7 PM). My symptoms only include vomitting only once a day at evening, feeling weak after breakfast (which my gyni confirmed to be normal), gas, usual slight cramping for 30 seconds to 2 min (which I believe is normal). My baby's heartbeat is normal and I have seen the fetus swimming and moving happily inside me :) .

However, just to get rid of this worry and anxiety, I would like to know the below :
a. Generally, is a miscarriage always associated with unbearable stomach pain ?
b. Would bleeding be before or after the pain and if there is clotting, how big would be the clots ?
c. If it begins with spotting how long would it take to show a heavy blood flow with other symptoms of miscarriage ?
d. What are the chances of miscarriage during 12th week, considering that the baby is healthy with good heartbeat and movements ?

I might sound really stupid but we have been gifted with a child after trying hard for 1.5 years. I am 33 years old.
I have gone through fertility treatments but failed twice (could not concieve). However, this time I conceived just naturally without any medicines !