With the stinging nettle - things can turn around quickly, like maybe in an afternoon. Pycnogenol takes a bit ... it is expensive, but seems to work well. All in all, I would give it 2- 3 weeks. If the pycnogeol is too expensive, go for the stinging nettle and the quercetin - both are relatively inexepensive. Claritin and similar were good for treating the typical symptoms, but as you mentioned did nothing for the feelings of lack of motivation, lethargy and really foul mood.
Also, if you are in the midst of feeling down and out, it may take a week or so to turn things around. One more thing ... I take St. John's Wort as well - prior to the allergy season, it has anti-depressant quailites, ... it doesn't make you happy or crazy, but it does lessen the down side of this allergy induced malaise.
So my general plan of attack these days is to start this treatment early ... just to be safe, about 1 month before allergy season typically starts. If you can expose your body to the allergen, without triggering a big immune response then your symptoms *may* lessen in the coming years. I keep this up until the first week of June or so, the weather here typically turns very hot and dry and all of the plants are typically scorched. I noticed that I am also hit by a mild wave of this malaise during the fall, corresponding with the late blooming plants like ragweed. With the fall allergies, I have no troubles as soon as the first hard freeze comes in.
I do have some moderate seasonal allergy symptoms - sneezing fits (sneezing continuously for 10 min) dark circles under the eyes and watery, itchy eyes. Sometimes my "treatment" works so well that I forget that I have allergy problems and forget ... my first reminder is the 10 min sneezing fit. =)
It still helps to less your exposure to allergens ... maybe sleep with an air purifier in your bedroom and make sure that you wash your hair nightly, wash your pillow cases and sheets frequently and if you have dogs which are outside, make sure that they get a frequent bath. This simply serves to help get rid of the pollen and allergens. i.e. if you have pollen in your hair, then put your head on the pillow, you deposit this on your pillow and you breathe it in all night.
Hope this helps!