Remember that Singulair is meant to control asthma, it is not an allergy drug. It helps keep tissues from swelling and restricting air flow, you have to use it in conjunction with another allergy med to get allergy relief from it. And it only works if you take it every day, it won't do you much good if you only take it occasionally.
Flonase also just shrinks tissues, no actual allergy relief.
I have found that many allergy meds have to be taken every day for about 2 weeks for your body to adjust and to see actual results. (This isn't true for fast-acting things like Benadryl.). For Claritin, Zyrtec, etc, you have to take it every day during allergy season for best effect. This can also help reduce side-effects as your body adjusts.
I'm not into taking a bunch of meds for no reason, but when it comes to allergies, I'd rather just take the drugs that work than be miserable.