Hi Fizzingfissure,
I'm so sorry you are having such a bad time with stress, your fissure, etc. Don't worry, you have come to the right place, where people know your pain, and can offer great advice and reassurance.
Now first about the tightness and inability to poop. Your stress is probably part of that - you are tense and desperate. You need to relax. Easier said than done! Have you tried taking a warm bath? That should help to relax you all over. Plus the heat and water will help relax the anal muscles. I was told to do that for my baby when she was crying with constipation, straining and miserable. I put her in a warm bath, and immediately the poop came out (in the bath - oops!). Lots of people here swear by sitz baths, which are pans of warm water you can put on the toilet and sit in.
So run yourself a nice warm bath, get in it and calm yourself down. When you want to poop, sit on the toilet and do whatever it takes to relax. Some people meditate. Some read a book. If nothing happens, walk around for a while. Maybe hop in the bath again.
Now, the diet. You mention increasing your fibre, but you don't mention drinking more water. It's absolutely essential to stay really hydrated. The reason is, the longer your stool stays in the colon, the drier it gets, the harder it gets. By the time you can pass it, it is dry and painful. If you get dehydrated, your colon conserves body water by removing it from the stool, so your job is to drink lots of water - several litres per day. I think everybody here would agree that drinking water is vital. Not coffee, tea, alcohol, coke, since they are diuretics. They make you pee, and rob your body of water.
About fibre - I would recommend more solid foods. Brown rice, quinoa, cooked vegetables, a moderate amount of white meat and fish, fruit (not bananas), oatmeal/porridge (I swear by my daily bowl of porridge). You can also take supplemental fibre like metamucil. Learn about soluble and insoluble fibre here:
http://www.webmd.com/diet/fiber-health- ... uble-fiberBy all means see your doctor. I think you could ask to be referred to a nutritionist, because it sounds as though a lot of your troubles stem from eating habits. I saw a colorectal nurse practitioner for my fissure, and she was really helpful with advice about lifestyle changes. I don't think doctors and surgeons are always great with those kinds of non-invasive methods.
It will take some trial and error, so keep a daily diary of what you eat and how you poop. You can use the Bristol scale to keep a record of how hard or soft your poop is.
http://en.wikipedia.org/wiki/Bristol_stool_scaleYou are aiming for a type 4! Diarrhoea is to be avoided! It is very bad for the fissure.
OK, I've said enough, and I know you will get other advice from people who've been where you are, suffered through it and are doing OK now. Hang in there! It's bad times, but it WILL PASS and you WILL be OK.