I have used all OTC allergy medications on my oldest. Zrytec worked great, but he was an emotional wreck. I took him off of it. Allegra wasn't as bad, but he still was having behavior issues, I just took him off of it, and it is night and day for him, total different kid. It took a good week to see an improvement while on either of those, and it was not an as need basis. had to keep him on it to see symptom relief, and it took me a good 5 days to wean him off of it to see his behavior changes as well.
I still have him on Omnaris (nasal spray, like Flonase) no behavior issues, and it helps with his cough somewhat, but our issue was a constant runny nose and sinus infections, it has worked wonders for that. I was told the nose sprays are more for relieving inflammation and congestion ( big issue with my little guy) and not to see much in terms of the symptoms ie runny nose, sneezing etc., but reducing the inflammation would prevent all the nasties from hanging out and then causing the sneezing, runny nose etc.
I was shocked the dr. prescribed Omnaris since he's 4, and all the leaflets I've read say 6 or above, but we only give 1/2 the dose. I was told I could use as needed, but it only seems to work for him on a daily basis. I plan on taking him off for the late spring/summer months since he doesn't have a problem then.
if the flonase was prescribed for your 2 yr old, personally I found it works best for my son with the least amount of side effects. I won't be using any OTC allergy medication for this kid, until he can describe what he's feeling like to me. But like everything, everyone responds differently.
Hope you find what works for your little guy!