How have I been making gold so far this expansion? Several ways, but my favorite is the Alchemy/JC cycle.
I originally picked Alchemy and Jewelcrafting for my main back in TBC because I did not want to rely on the AH to supply the metagems I wanted to cut and sell. The metagem transmutes back then required nine gems and four Primals and were on the Alchemy daily transmute besides. These days, the synergy between these two professions has only deepened and become refined into almost a pure cycle.
What is the cycle? You start with buying Obsidium or Elementium Ore off the AH - in my experience Obsidium Ore is preferable for our purposes, and the bot farmers have driven it down to 70g a stack on my server. Once the ore has been obtained, you prospect all of it with a goal of getting the uncommon Cataclysm gems. As mentioned in other articles, each one of these gems vendors for 5g by itself, or 9g if you cut it into anything at all. Rather than vendoring, we are going to use Alchemy transmutes to bake in some additional profit.
As with all things, you are going to want to check your own realm's AH prices to judge which direction you take the next step. The first thing I recommend is the Transmute: Shadowspirit Diamond. This transmute takes three of every type of uncommon gem, including Nightstones, which are likely to be at or around 100g apiece due to their use in leveling JC and the daily. Fortunately, the Shadowspirit transmute makes two metagems before any transmute mastery procs. Once you have these metagems you can either sell them uncut or cut them yourself if you have snagged any patterns by now.
The second option you have is to utilize the other gem transmutes to turn three uncommon gems of the same color + a few herbs into a rare gem of that same color (e.g. Transmute: Inferno Ruby). The uncut rare gem market right now is a state of flux given the lack of socketable gear for the majority of players combined with a lack of JCs with the appropriate cuts. What this means is that you are not likely to be able to make much of a profit off of selling uncut gems - this state will naturally correct itself over time to resemble what we all remember from epic gems at the end of Wrath. The good news is that cut gems are probably going for 100g+ minimum, turning those three somewhat useless carnelians into, say, Brilliant Inferno Rubies which will sell for 7-9 times as much as the vendor price.
As a sort of thought experiment, imagine that 10 stacks of Obsidium Ore at 70g a stack gives you enough uncommon gems for a single Shadowspirit transmute and two other rare gem transmutes. If you are able to sell the Shadowspirits (cut or uncut) for only 350g apiece, you come out even before considering the rare gem transmutes (cut or uncut), not to mention any rare gems gained by prospecting and/or excess uncommon gems in quantities below three. Odds are good that you will be gaining more than that, widening your possible margin and allowing you to maintain a profit in case Obsidium Ore prices higher on your server.