DO please, try and get a second opinon if you can!

It will give you and idea of what all has been going on and what to expect in the future. It will likely mean a lot more tests? But it is definitely worth the effort! Get an handle on things and go from there.
As for Gabapentin? It and I did not get along well at all. I tried 3 more of about 50 pn meds before I found one that worked for me… I can attest that the neurontin did cause for me, severe muscle spasms, as it can deplete a lot of calcium. Try taking a calcium citrate w/Vite D and magnesium combo and see if that helps. There are nutrition and vitamin shops that sell these and some are even reputable! Any web site that clearly posts the ‘ingredients’ is likely better than those who say ‘secret formula’ and make all sorts of claims for cures. Once I got off the neurontin/gabapentin onto another med and started the calcium combo the ‘tremors’ subsided greatly.
Before going to another doc? Get copies of past medical records ‘for your files’ and go see someone else. Be careful tho? Don’t bad-mouth a prior or current doc, just say: We aren’t connecting or communicating well. Leave it at that.
I hope this helps and that things don’t get worse! I for one, deal with that fear every day. But, as Dan says? THIS DOES NOT HAVE ME! Hope and good things soon!