I download Hearthfire then suddenly after i finish Dawnguard you know where the vampires attack towns and stuff well it all suddenly......stop either it's a bug, glitch, or a really really good thing lol

Probably a conflict between the two dlc's.

I figure because after i download Hearthfire the attacks went like this for me:
4 vampires
1 Mysterious Traveler
1 Vampire and one Vampire Attack Dog
and that's it after that

Its not a bug. Random vamp attacks stop after you complete the DG questline. They only then happen if you force them to (ie block the sun).

With Hearthfire being a completely separate thing from DG I'm not surprised something like that happened.

This as well.

Your first post was kind of confusing. What I got from it was you finished Dawnguard and now the Vampire attacks are no more, correct? Well upon completion of the Dawnguard questline the vampire attacks are meant to stop.

Unless the OP meant that it stopped before the end of DG questline.

If that is the case then it would be a glitch/bug. For some a blessing.

Well he did say "suddenly after I finish Dawnguard" then he goes on to explain how the attacks have stopped so I'd assume it happened after completing the questline.

The vampire attacks stop once you complete Dawnguard, that is if you do what Lexandro said and block out the sun. I have noticed that my textures have become smother and sharper since I got Hearthfire though.