Your body makes it's own vitamin D if you just get out in the sun 15 minutes or so a day. It's spring now in the US, shouldn't be hard to get out a bit.
From what I've read, and I'm no doctor, 10,000 IU a day is toxic.
I haven't heard of vit D for allergies, but it does help your skin get rid of bruises that don't go away on their own. (My spouse used to have heme brown spots from bumps which went away when I got him on 2000 IU daily for a few weeks.) I don't know of any scientific studies regarding allergies, and forum opinion certainly isn't scientific!
Get tested for deficiency, simple blood test. I am low most of the time, don't go outside enough, take 2000 IU in summer, 4000 IU in winter. If I do get out in sun for a good time I don't take any that day. Your body doesn't store D. Study I read said that for every 10 units of measure (don't remember what that was) you are low in blood, you need 100 IU of D in capsule or pill daily. (You should be able to search that one.) I was at about 18 (in winter), needed to get up to 50 or so.