There is no one right answer. I have seen so many paths for someone to become a coder. It seems like you are currently pointed in the right direction.
Here is my personal opinion.
Whether or not getting RHIT certification is the right move for you depends on what you want to be doing. RHIT generally opens more doors for non-coding, but related positions (cancer registrar, revenue cycle data reporting, compliance, etc.)
If your goal is to be coding exclusively, I don't think RHIT is a good use of your time and money. Most coders I have come across in my career are not RHIT certified. If a job will only consider someone with experience, no amount of education replaces the experience. Not all jobs have the same experience requirement.
Getting your foot in the door with a Patient Access Representative position seems like a great move. Why you haven't been moved to another position in 1 1/2 years is the key question here. Most large companies are good about moving up their stellar employees. Perhaps you don't interview well. Perhaps your boss gives a less than ideal review when contacted by the hiring people. Perhaps on your second day, you accidentally parked in some manager's spot and they have it out for you. Some jobs only consider transfers after you've been at a specific position a certain amount of time. Maybe the Patient Access Representatives have a bad rep for being nincompoops or rude or drama queens. Or perhaps you just haven't found the right fit yet, and the next interview seals the deal. If I were you, I suggest:
1) Speak with your current manager and make sure they know what you are looking for and could be an ally in your quest. Ask if they (or another manager) will do a mock interview with you to help guide you. Sometimes great employees are just too nervous during an interview and seem like a bad decision to the hiring manager.
2) Try reaching out to the managers you interviewed with and ask if they are willing to discuss why you weren't a fit for their position.
3) Network, network, network within your employer. Anytime you happen to work with someone from another department, be extra friendly. Go out of your way to help them. It would be great during an interview with that person's manager to relay that you worked well together.
4) Perhaps the problem is your current employer, for a variety of possible reasons. You may need to look outside your current employer.
5) Network, network, network outside your employer. Join your local AAPC chapter and be active in it. Get on a first name basis with other members who work either inside or outside your current employer.
6) Since you are not currently coding, make sure you stay up to date on changes. During an interview for professional fee coding, you should know about the outpatient E/M changes that took place for 2021. It's easy to lose the skills you previously acquired when you don't use them. When hiring (whether coding or billing), I don't mind someone without experience, but if they finished their education 4 years ago, and can't give me an example of when to use a modifier, they are not getting hired. For example, this is your first post on the forums. Even if you're not responding, it's a good idea to see when there are significant changes/updates. Telehealth in March 2020. Outpatient E/M 2021.
7) Your resume AND coverletter should be spot on. The person who reads it should want to call you for an interview. If you are not even being interviewed, that's the first thing I would look over. If you interview, but are not hired, then it's less likely your resume or coverletter. I recommend having a few different coverletters customized to the position you are applying.
8) GOOD LUCK!!