Look, if you have a fissure, the only treatment I know is surgery, because I had to have it done many years ago. Get yourself to a doctor who can diagnose this, because a fissure is a physical tear, not something that will heal with fiber. Softening the stool will help ease the pain, but it won't cure the problem if it is a fissure.
Try a probiotic and Metamucil. Eat an apple every day. No soda. Drink water instead. Filter your water with a Zerowater pitcher if possible. It takes out more of the toxins like chlorine than any other. Avoid straining. Try glycerine suppositories to start things moving. Walk and stretch, including ballet stretches where you bend your back sideways. If these measures don't work, try Miralax. If even that doesn't work, then you will need to see a doctor.
You can take Dulcolax now and then, but I wouldn't use it more than about 3 times a year. It can damage your colon lining if you take it too often.
Have you tried taking fiber? If that doesn't help see a colon/rectal doctor
Sorry I have posted this to the wrong community, however any suggestions would be very grateful thanks