20 days enough????

I wouldn't switch until at least a month.

(and..really, it can even take longer before there's a 'difference')

So maybe give it a little longer, and then add something else to the doxy...or switch to Minocycline...or Ceftin..and then after a couple weeks, add a macrolide maybe (biaxin or zithro)?

....or if you're wanting to target Bartonella, you could add Rifampin....
Rifampin will go with doxy (although Rifampin may reduce the effects of doxy somewhat)....or Rifampin and minocycline...

There are many combinations.

Have you thought about subscribing to LLMD MR "TreatLyme.net"? it's a small fee monthly...you could subscribe for one month and then write down all the protocols...if you can't afford to continue with the subscription.

If you are working on this alone, just be careful with Tinidazole, it can damage nerves.
And don't forget to take probitics regularly

I agree that 20 days isn't enough treatment, especially since you are dealing with chronic Lyme.