What might be the cause of random Finger Twitching?

Hello, just wondering if anyone can give insight onto random finger twitching? Worried that it's early-onset Parkinsons. It's mostly my pointer finger and thumb twitching randomly without me doing it, and when it does I can feel a sensation in the nerves up the arm in question. I've had random muscle pulses my whole life (which I assume is benign fasciculation syndrome) all over my body and have had gastrointestinal problems (kind-of constipation, more like delayed bowel emptying) for six years. I'm only 21 but am worried that this is a sign of early-onset Parkinsons; I know constipation and tremors (is this a tremor?) are early symptoms.

I know I kind of sound like a hypochondriac but I'm desperately trying to find out which tests I should prioritize. I'm not made of money and the possibilities of my conditions are far-ranging. I'm scheduled for an MRI in August but my neurologist didn't even acknowledge the finger twitching when he heard my symptoms. So if anyone has any insight, I'd appreciate it. Thanks.