Tourist visa and transit visa

Hi!

I am Serbian cityzen, currently in Pokhara where I will stay till April 2014.
May I get in KTM tourist visa for 90 days and in same time transit visa?
Here is explanation why I need it:
- I should fly to Beijing next spring to renew my passport in Serbian embassy in Beijing
- I must wait for about one or even two mounts for new passport
- While I will wait for it, I'd like to go in Mongolia
- I read that is no possible to get Chinese transit visa in Mongolia
- After Mongolia I must come back in Beijing and pick up my new passport
- That time, I will not stay over 10 days in China because I will continue to South Korea
I know that 90-days visa with double entry would solve my problem, but when I asked in Chinese embassy in KTM, they said there is no possible to get 90-days visa with double entry, only with a single entry.

Hope you understand my not so good English.

Thank you in advance!