Yes I am thinking gluten too. And something else....

But fast transit can also cause this. When there is too fast a movement thru the bowel, the fat cannot get absorbed properly.

Do you drink or consume food with high fructose corn syrup?
I had a hidden fructose intolerance for years...which became a crisis about 2 yrs ago. It caused a very fast food transit, and issues similar to your GI issues. If you stop eating all sweets and do not drink any juices or eat fruit for 2 weeks, then see how your GI is doing then. This is also part of a diet that starves Candida (yeast). If you developed a dysbiosis in the bowel, from the long term use of antibiotics, then the Candida can be causing your problems.

Also I'd try right now, Benfotiamine 300mg a day (you can take this all in one dose as it is long acting). iherb.com has this at a reasonable price. If you prefer something easier to obtain, try 300mg of Thiamine (B1) daily in divided doses.
Candida releases alot of aldehydes into your system and metabolizing them uses B1 heavily. By increasing B1 you can reduce this load. Elevated aldehydes give neuro symptoms..similar to what you describe. Most mainstream doctors do not test for this. Do you recall having a test that reports for Candida?

It is very possible that the Levaquin is doing more than one thing to you. Most surely all antibiotics can cause upsets in normal bowel flora. A good probiotic, or a good yogurt like Stonyfield daily, may also help you with the GI issues.

Also for the time being, I'd reduce the GLA to every other day or every 3rd day. Too much of this increases bowel transit in some people--sometimes even diarrhea.

There is another risk with Levaquin, that may take months or up to a year to manifest. This is tendon injury. Some people get frank tendon ruptures. The mechanism is not understood at this time, just that it "happens". So do not over stretch or engage in activities/sports that stresses the tendons. The Achilles and knee tendons are the most often affected.