Neither 1 nor 2 is natural. You'd say: I'm running a 38.6 degree fever. or I'm running a fever of 38.6 degrees. 3 is fine. It's normal to use the present simple (is) because this is an undisputed fact - a date on a calendar. There is no need to use the 'going to' future, because it's not an opinion, plan,intention or prediction. By the way, 'gonna' is not a tense. You shouldn't write this unless you are transcribing deliberately informal speech, for example in a subtitle, cartoon caption or song lyric - or possibly in a brief text. Please don't make the mistake of assuming that this is everyday written English.

Thanks for this! Yeah, it is interesting!

Heh heh heh.. of course I imagined it was more likely a typo than an attempt to revive Old English. Still, my pre-Danish theory is more interesting. :)

Thank you Phil. Actually I just made a typo. However, I think the title may not be changed even if you edit it:)

In Modern English, the 3rd person singular pronoun is "they" -- the word "hey" (used in Old English) was replaced by "they" due to Danish influence, and because "hey" sounded too much like "he."