You are fortunate to be tolerating 25mg DMSA doses! It took me 3 months before I could do that.
If you have a candida problem I'd be surprised if you could tolerate more than monthly rounds with DMSA. It definitely makes candida problems worse. There are things we can do to minimize the problem but most people in that situation try to get DMPS. It is generally quite nice to use in the early months. Cutler's view is that DMPS only needs to be taken every 6 or 8 hrs.
Honestly, I think it would be insane for a person with candida problem to try 50mg doses in the early months. Doubling the dose does not double the excretion according to Cutler but it usually doubles the sfx!
Cutler says thiol chelators can be taken with or without food.
When I feel a dull headache especially in the front of my head, it suggests too much redistribution of Hg. Taking doses more frequently and taking more vitamin E resolves that for me.