I recently just downloaded Dawnguard. It awesome but what's up with the bugs?!!! It keeps freezing. Especially in combat. I haven't noticed if it freezes only when Serena is around but it's continuously freezing. Are you guys going to fix the bugs? Please!

No freezing - I have played it through, completely (twice) and it doesn't freeze on me ever.
If you're on PC you need all the Unofficial patches, and use BOSS.
Probably clean things with TES5Edit (wherever BOSS recommends) too.
If you're on console... I dunno.
Sorry; wish I could help more.