This may be a little disjointed but I will give it a try.
First, as I understand it, you are taking only sinemet at present and that in the standard release form. The other drugs mentioned are either tried and discarded or are potential add-ons.

If that is so, then you are getting little or no benefit from the sinemet. It takes an hour to hit your system, spikes, and is gone by the two hour mark leaving a little pile of waste products behind. The levels in your system are never getting to a point where you know if it will help or not. Instead, you are being jerked back and forth.

I don't give medical advice but I will tell you what I would try. (This will need to be coordinated with your doctor because you are going to use up some pills at first.)

I would take ten of those sinemet 10/100s and crush them and dissolve them in a liter of water. Then I would drink a tenth of the solution and repeat that dose hourly until I began to notice an effect, either positive or negative, at which time I would drop to two hours for the next dose, three for the ones from there on. Keep meticulous records. What you take, when, and how you feel on the hour.

Somewhere along the line you should notice improvement, even if only for awhile (as might happen if your dose gets too high - in which case you increase the time between doses). If you do not, then your diagnosis needs to be looked at again. If you do improve, then your notes will give your neuro a place to begin.

During this day of experimenting, eat very plainly. Just fruit and nuts is a good choice because some food additives as well as excess protein can cause some of the problems. Once you have this baseline, however, you can start tweaking things. Good luck. -Rick