Slow Large Bowel Transit

Genna • 20 years old. bisexual
On Christmas <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Eve</a> my local doctor gave me the results of my colon transit scan (test ordered by my gastrointestologist) and I was told that I had slow transit in the large bowel. I don't know much about this can anyone explain it to me?? Can I fix it?? Did I do something to cause this?? 
I always cramp up and have pain and it's so uncomfortable!
I have had constipation for as long as I can remember (I am 16). I constantly get stomach pains, I get nauseas and vomit and I get extreme reflux all the time it has gotten worse lately. 
I have been put on a syrup laxative (prescribed by my GI) that I have been on for a week and it has worked once which was the first night I took it and I have also been put on a Fleet Enema one weekly for two weeks. I have had heaps of different laxatives in the past but I keep having reactions to them so now I have to be careful on what ones I have. And Anti-acids for reflux and iron because my iron has dropped AGAIN! 
I had the first Enema on Saturday night and it work instantly but it only worked once and it really hurt my stomach. The next day I was constipated. Monday I went three times and then on Tuesday morning I woke in excruciating pain all over my stomach I could hardly move! And I had got my period the night before. The pain lasted until last night. I went to the doctors today and she said it's just constipation and she up the doseage of the laxative syrup.... Still no movement and it was taken four hours ago. 
I also get extremely gassy and it smells like something died inside of me it's so embarrassing. I can't live like this!
Just to bring the top bit down: On Christmas <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Eve</a> my local doctor gave me the results of my colon transit scan (test ordered by my gastrointestologist) and I was told that I had slow transit in the large bowel. I don't know much about this can anyone explain it to me?? Can I fix it?? Did I do something to cause this?? I won't see my gastrointestologist until February :(