I'm a 20 year old male, not overweight, and I've recently (in the past few weeks) developed concerning symptoms.
For a little while, I was having looser-than-average (not quite diarrhea) greenish colored stools on and off. Not too long afterwards, I became moderately constipated. I alleviated this with the aid of stool softeners (for three days), but stopped because all of a sudden I was getting cramping pains and discomfort in the abdomen.
It's been almost ten days since then, and I've had the following symptoms that vary day to day and hour to hour and seem to overall be getting worse:
- cramping and flatulence when I first wake up in the morning; relief brought by a bowel movement of fairly loose, pulpy brown to green stools. I have one bowel movement per day.
- noticable lower abdominal "tightness", distension and discomfort. It's like my bowels are swollen or full.
- light to moderate itching, stretching, crampy pain that crops up in varying parts of my mid to lower abdomen. The abdomen is also slightly tender to external pressure.
- a tiredness of the abdominal muscles, difficulty flexing abdominal muscles with pain
- symptoms sometimes worse after meals, especially large ones
- aortal pulsing around navel seems more obvious
- symptoms exacerbated by fast or quick movements (ex: twisting quickly, jumping)
- recently, fatigue

I'm worried that I've suddenly developed IBS, or the medications I took for my bout of constipation harmed my colon. Is some sort of malabsorption behind this?

I've haven't changed my diet except for adding a slightly greater amount of fiber.
I regularly eat sushi; could a fishbourne parasite cause these symptoms?