There is no easy answer or magical tricks that older/experienced parents are withholding from you. Its more of setting a positive and respectful environment for the trainee.
Several months ago my 2.5 yr old was home for 5 wks with out daycare so I jumped on the chance for some toilet training. Having messed up a bit on her older brother a few years before I equip myself with "Diaper-Free Before 3: The Healthier Way to Toilet Train and Help Your Child Out of Diapers Sooner" - awesome book that most of my toilet training specific opinions are based and very worth purchasing. Here a few things that can help set the stage for success:
Verify that his stool is soft and he isnt battling constipation too. Set up a routine and be consistent. With regular activities and regular meal times, more than likely your son will have a regular BMs. Have bm chart or whatever is needed for you to to know when he needs to go.
Going to the bathroom is a normal part of life - Just like drinking water. Stop all crazy incentives and when its time or when you see the cues, tell him its time rather than ask him if he wants to go.
Even though my daughter could use the big toilet she much rather enjoyed the little own that was a feat of climbing and that her feet could be firmly on the floor. Its not nice to clean out, but imagine yourself going a toilet that was big enough for you to fall into and that was as high as your tummy and you couldnt touch the floor. Also, you can model for him since each of you have your own toilet.
My older child had troubles defecating setting down. He had to start by sitting on the toilet, in his diaper, at anticipated times so he could get use to the position. Being physically comfortable is going to be very important.
Little kids have control over so little of their life. Something like defecating
or eating a certain food can be something the a child has realized he has control of. Its in the context of the control that you need to get rid of the incentive programs, but also any negativity or punishment associated with going to the bathroom (including genuine disappointment from having to clean up an accident, shield your son from those emotions). Every kids seems to want to be "big" - just let using toilet be a something big kids do, something that mom does as a regular part of like. Get rid of all the angst and specialness and the whole big deal factor and your son may give up some of that control and move on to other things, like what pjs to wear.
Get your son in on it. Cant have a positive experience with out his co-operation. For example, my daughter and I pitched her remaining diapers together. We both were committed. I kept some night time pull ups and for the first few weeks she preferred wearing them at night. After a while, she wanted to wear undies, so the choice was hers, use the toilet before bed time or wear a pull up. She was invested in the training, not just me.
If the above attitudes jive with your parenting style, go buy that book and you will get more detailed explains of why each matters along with a brief history of life be fore disposable diapers.
Good luck and find the needed patience somewhere. Dont worry too much either (doesn't help you and your son will soak it up), the situation really is an individual experiences and is not going to be exactly the same as others.