[IssuAga]

1.) If I'm trying to express yesterday night, can I use "昨日の晩" and "ゆうべ" interchangeably? Or does it depends on the grammar?

2.) The word "毎月", can be spelled using both　"まいげつ"　and　"まいつき", but which of two is more frequently used? Or does it also depends on the grammar?

3.) The character "さ" used in words such as ”さ来月”、”さ来年” appears to be "再" whenever I type it out, such as "再来月","再来年" and so on. Is there any rule regarding when should the Katakana characters be written in Kanji?

I often run into above situations when I'm trying to read short sentences, so I'm wondering whether or not there are some general guide lines to follow.

Thanks.