I had a similar experience as you, in fact my problem started in 2000 in Houston, too, go figure. As you know, the Neilmed works well, but it only reaches the lower sinuses due to gravity. I developed the Flip-Turn Sinus Flush, which does reach the upper sinuses. The Grossan Irrigator may reach them too, but I don't know as I've never tried it.
http://www.medhelp.org/user_journals/show/2322
The Flip-Turn Sinus Flush is mildly risky, because you have to bend over to do it, preferably in a shower, but you can also do it outside on soft ground. The Neilmed solutions will do just fine.
I assume that you are already under a doctor's or allergist's care.
You may also wish to try nettle leaf capsules for at least 2 weeks, for the allergies. In the feedback I've received, it seems to be very effective for about half of the people who try it, with no known side effects. I'm not big on herbals anymore, 'cept that one. BTW, I still have perfectly clear sinuses and no more allergies. I hope you have similar luck.