That is one of the limitations of a DPD chlorine testing kit --- DPD can bleach out at high levels. It may be that you have had chlorine at times when you've tested but it is just bleaching out the reagent. Go to Walmart and pick up a cheap OTO/Phenol Red kit (yellow and red drops). It will not bleach out at high chlorine levels. Use it to test right now while you are working to clear the pool. You can use the chart at this link to help decipher readings that are higher than will show on the OTO kit. http://pool9.net/oto-chart/

If your pH is registering 6.8 on your kit, it could actually be much lower than that since that is as low as the test will show. Add bigger doses of Borax until the pH starts moving. Add a half a box at a time. Test two hours later and add more. Keep at it. Low pH is a critical issue as it can damage your pool. I'd probably buy about 4 or 5 boxes. If that is more than you end up needing, it doesn't go bad.

It would probably also help to bring your TA up some. Aim for 80-100ppm. Add a couple of lbs. at a time, wait a couple hours, retest, redose. It is fine to add Borax and baking soda one right after the other with no problem.