Possible parasitic infection

For the last four months I've been suffering from a slew of symptoms, including dizziness, (most distressingly) mental fogginess, extreme fatigue, muscle aches, and intermittent stomach aches. I've been tested for just about everything and all tests have come back negative. However, just recently I remembered that a week before this all started I was hiking in southern Utah and drank some untreated water after I lost one of my water bottles. It's a long shot, but does anyone know of any water-borne diseases or parasites that can present with primarily mental dysfunction and muscular fatigue but *not* classic signs like diarrhea?