Grrrr Please Help!!! post/ page problem

Hi all.

I’m really hoping someone has the answer…

Basically i have a wordpress site and have create quite a few pages on my website to do with acne.
When these pages rank in google i see the title (e.g) Best over the counter acne treatment.

I am now wanting to start just creating separate individual posts on my website similar to a page, this is because of a new theme a brought.
Anyways i have noticed since i have been creating the posts and they have been ranking in google and the title what it now show in the serps are:
Best over the counter acne treatment | Acne on chin acne

no longer just the “Best over the counter acne treatment” It seems to have just added the name of my site to the end of my post titles, the pages never did this.
I tried to use all in one seo pack to just show the” Best over the counter acne treatment” but no luck.
I really want to just have my title name and noting else. is this with posts or will it always look like that in the search engines?

Also does anyone know if google ranks higher posts or pages?

Hope someone can help ??