Constipation and Colon throbbing HELP!?

So I'm a 19 year old female, I eat healthy and work out 3-4 times a week. I've been having bowl problems for about 6 months I've been pooping every other day. Until this past week I didn't make a bowl movement for 4 days. I was getting pains and feeling bloated, my left side throbs a bit and it was starting to hurt down my leg also. So I went to walmart and bought a fleet enema and used one bottle. I exploded but still felt stuff in there and tried to push but it hurt. I've been eating a lot more fruits and vegetables and fiber and drinking lots of water. Its been 3 days after I took the enema and I haven't made a bowl movement yet. So I went to the doctors today and he said i'm not getting enough "soluble fiber" Although he didn't even check my stomach he just sat at his desk. He proscribed me with Miralax and told me to take it everyday and give it 1-2 days to work. I took it earlier today, nothing has happened, I feel like i'm going to pop, I feel sick (I don't have a fever) I push and nothing comes out. My lower left stomach hurts i have a few bruises around the colon area on my stomach.and i'm getting throbs randomly on my left side. :((( idk what to do!!!