I tried Zoloft for 3 months before switching, my guts never were able to tolerate it. If it's not doing it for you and you gave it a fair shake, I suspect you can probably find something that will get you from a 5-6 to a 3 or so.
Monotherapy is generally considered more likely to succeed than combining medications because it is very difficult to determine what is working, and why, when several are used simultaneously.
Perhaps trying a different antidepressant that you can tolerate at the higher end of the therapeutic dose range may be more effective. Since you are having trouble sleeping, a slightly sedating TCA (amitryptaline, clomipramine, there are perhaps several others, but I can't remember right now) may be very helpful.
It is often best to start on a split dose, 3x per day, and you can start at a VERY low dose compared to the therapeutic dose. The start up side effects that can raise anxiety levels to 8-9 out of 10, are, generally speaking, not there with TCAs. At least not to the same level as with SSRIs. The initial slight sedation, which goes away as the medication becomes effective, is often just what we need to reduce the anxiety level. In fact, oddly enough, in my own experience, I would go from baseline anxiety down to almost nothing within 1-2 days as the medication levels increased and I became slightly sedated. Like a honeymoon period, the anxiety would come back to almost the old level, but over 2 weeks it would return back to near the honey moon stage.
I can say with near certainty, it wasn't until I found the right medication at a proper dose that I felt ANY real relief from anxiety, aside from benzos. I spent 2 years battling ineffective medications, start up side effects, and withdrawals which made me see what my anxiety could be at its worst. Finding a med that works, is, in a way, coming full circle.
Good luck! Hang in there! You will find relief.