I'll lend a few suggestions here as someone who has started, operated, and sold detail businesses (with some success) twice before entering into the manufacturer/supplier side of the business.
First things to think about is your approach to the market - certainly FB ads, listing on CL, flyers, business cards - thats all fine and dandy, but how about reaching out to local car clubs, offering to do an education day for their members on the importance of detailing, what processes you offer, etc? Approach local businesses and offer your services on a recurring basis - "I'll be in your lot the first Tuesday every month and offering express details for $xx.xx with advanced booking". Visit used car lots and offer up services. Network as much as you can. Think outside of cars - with a pressure washer and a mobile service you can do things like power washing windows on homes/businesses, cleaning decks, etc. FIND ADDITIONAL MARKETS YOU CAN SERVICE.
Another consideration, and something you didnt' specifically call out, is what kind of services are you offering. I personally hate the term "detailing" its become too broad and unregulated of a term. Are you trying to do full correction only jobs for $700 a whack? If so you're not going to get far. That market is small. If you're looking to be busy think about volume. Offer everything from a basic express wash and hand dry up to 1 step corrections. 99.9% of the world doesn't care about a perfect swirl free finish. Clean is good enough, so cater to the masses. Offer them what they want, not what you want to sell. In my first detailing business, fully mobile, I would make a killing on days where I lined up express washes... offering high quality, thorough cleanings. I could easily do 15-20 of those in one day. Get these people comfortable with the idea of regular appointments, once a month, or 2x a month. Create a steady stream of repeat business - if you're not getting repeat business from the customers you handled 5 months ago when you started then you either didn't provide the service they expected or you failed to follow up with them about maintenance.
One last thought - you started a business 5 months ago. I've been in this industry for 17-18 years now and I'm a young pup by most standards. Don't expect overnight success and don't expect detailing to make you wealthy. Its rare to make a full time living off of detailing, especially in a short period of time. If you're doing the job right, making customers happy, then over time your customer base will grow and (they should) become repeat customers. If you added 2 new customers a week, and didn't loose any... at the end of 5 months you'd have 40 customers. If you can get half of those to subscribe to a regular maintenance program you've got 20 cars to detail a month and growing by 1 or 2 clients a week. Success is not found in the 'one and done' customer - its found in the lifetime customer.