I have learned a great deal about this and found what works above all things from experience and very very wise advice.
Yes there is evil, both outside of us but moreover already WITHIN us. Everyone has "evil spirits" within - they are referred to in the new age as the "ego," but more accurately as "egos" in modern gnosis, also seven deadly sins, red demons of seth in egypt etc etc etc.
Our silent awareness or consciousness is the real us - the thoughts and emotions, drives, impulses etc are from the egos or sometimes external "spirits" who influence them. The internal egos are really just part of natures program of the animal kingdom but "evil" because they are ultimately destructive to us. They have developed more complex because of the mind.
They exist separately and can be seen sometimes when having an out-of-body experience, and certainly enter our minds as thoughts. Children can sometimes see them as ghosts while falling asleep and many adults can clearly hear the voices while going to sleep too.
They enter our body in different places depending on the type (thoughts enter the head, emotions enter the heart or solar plexus, motor function at the base of the head, instincts in the lower spine, and lust in the groin - this is important to remove because it's so powerful and can create strong entities called succubi and incubi, however sexual energy itself is divine and so should be used for spiritual not animal purposes)
It is possible to destroy ego's with intense internal prayer but to the female aspect of God, the Divine Mother. Whenever these voices are present ask for them to be disintegrated or however you feel more comfortable asking. This has the potential to change your whole being if you use it whenever you are not in awareness (this is part of the real way to become like Jesus, but meeting him would certainly be helpful)
External Spirits -
Because this all started from visiting a "spiritual" expo, you probably have been attacked by negative forces, because most people there are channeling or going along with negative forces believing them to be good because they sound good or know of certain truths.
In this case there are phrases that work to send them away, from the Christian "our father" prayer and prayers of other religions, to others learnt while out of the body taught in gnosis, but one of the best is getting yourself a plant called "agave americanum" or "century plant" which has always been used as protection for 1000's of years. You can ask the elemental of that plant to protect you, and it certainly does, although it sounds crazy.
I have tried all of these and found them to work very powerfully, i have even consciously fought demons while out of the body and have changed internally alot overcoming many personal defects etc.
The best and most sensible group i have ever come across that changed my life are GNOSTICWEB.COM who teach free courses and have forums etc with many experienced people giving help on many topics. I really recommend visiting to attend the forums or do the courses which is where tried and tested information is given in detail. Better yet it is a non-profit organization, so no one there is motivated by money, which is comforting :)
Although your situation is negative at the moment, it can open the door to a much larger world...