Recently on skyrim I have been finding loads of bugs which I have never really found so many before, for example a quest items are not on corpses and 'find evidence' I take the evidence and it does move the quest along, it's very annoying. Can someone help.
I also have some mods but mainly horse ones.

Well, the game does actually have bazillions of bugs. If you haven't installed Unofficial Patches yet, you really should. They exist for a reason.

You may need to revert to an earlier save to fully prevent quest related bugs from occurring.

As Kirottu^D mentioned above. Actually, those bugs and glitches can happen randomly. They can't affect your first game-through, but can occur on a second one. !!!

If those mods you are using, *are compatible with the USKP, then you should definitely install it. (*you can check that, on the installation description of your downloaded mods)

After you install the USKP, go and load a save before the glitch happened, and then make a new manual save.

load the save, wait for (31 in -game days), and make a new save again. Load that last save, and proceed from this point on...with your game.

Make sure SKyrim is fully patched also. If you have a good Internet connection, this should have been done already.