Spelling ikkagetsu

I said to my IME to spell いっかげつ and to my surprise it
didn't show 一月 but 一ヶ月. My astonishment is build
up on following bases.

1. I expected いっかげつ to be 一月 the same way as
いっぴき will be 一匹, with no extra "thingies".

2. Let's say there will be extra "thingies". Why, oh
why not use hiragana, i.e. っ?

3. Why is there an option of ヶ　what so ever? What
happend to ヵ as the only available option?

--
Vänligen
Konrad
---------------------------------------------------

Sleep - thing used by ineffective people
as a substitute for coffee

Ambition - a poor excuse for not having
enough sence to be lazy
---------------------------------------------------

.