@pawngobbler I will also reply just for an additional point for you. I contacted my Rep first (who did nothing), then my Senator. Their office was much more helpful and got me to a person who does this regularly. She had me fill out a form, but I will put copy down an altered version of what I wrote:
"Dear [Senator]'s office:
I write to your office regarding my security clearance application.
I accepted a contingent job offer with [contractor] in [date]. This was contingent upon receipt of a DoD Secret clearance, and I am unable to begin work without clearance. I applied immediately, submitting my SF-86 in [date]. In [date], I was notified that I would not receive an interim clearance (eligibility pending). A few months ago, I reached out to [Representative]'s office but I do not believe they have taken action on my request. I am currently working part-time while waiting for clearance, and today marks day [number] of waiting.
I would appreciate if [Senator] could inquire the DoD about the status of my clearance investigation, and if possible, request that the remaining stages of my investigation and adjudication be given additional priority.
I thank you for your time and consideration."
Note that they will want to know: the employer, level of clearance, which agency you will be cleared under, how long you have been waiting, and if you have already contacted another Congressperson’s office.