If your business does not show a profit after a few years, the IRS may question if it's a business or a hobby, but profit is not the only consideration.  This article on the IRS website offers 9 factors to consider:  How do you distinguish between a business and a hobby?

The main (perhaps only) difference, tax wise, between a business and a hobby is that with a hobby you can deduct expenses only up to the amount of the income. 

To decide whether your photography is a business or a hobby, you should also read this short article on the IRS website:  Hobby or Business? IRS Offers Tips to Decide   If, after reading what the IRS has to say, you consider your photography a business, continue to treat it that way on your tax return and include it on a Schedule C.

I’ve already decided that it’s time to convert it to a hobby. I’m just not putting enough time into it to justify another year of losses. My question concerns how to file this. Do I file 2018 as a business again but just mark that I no longer have it and then report as a hobby for 2019 or do I just not report it as a business at all for 2018 and go ahead and report it as a hobby on this tax year (18)?

Report it as a business in your 2018 return and indicate in the General Info section that you stopped the business in 2018.

Next year, you can report your Hobby Income under:  Income & Expenses > Less Common Income > Miscellaneous Income, 1099-A, 1099-C Hobby income and expenses > Hobby income and expenses