IBS? Pulled Muscle? Or should I be panicking?

I have been suffering from health anxiety for years. It seems every few months I develop some sort of symptom, and I often Google about it (I know...I know...) and well, you know the rest.

The latest issue is bowel related.

I have been having a dull ache/discomfort on my left side since September. This has been off and on. I seem to recall only having been concerned about it 2 or 3 times since that time, so that proves to me that it comes and goes..as if I have had it constantly, I would have been freaking out constantly.

The thing is, I know exactly when this problem started. I was out of town for business meetings, and I was on my way home from dinner. I needed to use the washroom badly, but I was not back to the hotel yet, and I hate public washrooms..so I held on and put myself through punishment for about 10-15 minutes until I finally got back. By the time I got back I felt I had to now push or strain myself to finish my bowel movement. I was in a rush as I had to meet with some colleagues in the lobby to go over a project for the next day. While I was straining, I felt a sudden pain in my left side. (No bulging or anything, so I really don't think hernia)

Since that time, I have had this ache/pain off and on. Its mostly on my side, but sometimes can radiate towards my back or my front. I also find that when it is 'flaring up', that it is usually relieved by a bowel movement. Is it possible that I pulled a muscle in September, and when my bowel is full it sometimes aggravates the muscle?

The reason that I am posting this today however is because for the past couple of days I had had some symptoms of what I believe to be constipation. I have read online that constipation is when you don't have a bowel movement more than a couple times a week...but I have at least one every day. It's just I often feel like I'm not really finished after I do, and I have to strain a little too much. All of these new symptoms seem to have started after January 1st. On January 1, I was rushing to go to my aunts house for a potluck supper. I went to use the washroom and was having a normal bowel movement. However, it seemed endless. I was running late so I began to push and try to speed things up. Is it possible that I re-aggravated a muscle and thus why I'm sometimes feeling my left side again this week?

I also sometime stress over the ache in my side, and I have read numerous times that stress can cause a lot of symptoms.

To sum all of this up...

- I am 28 y/o male
- I strained myself on September 29th while having a bowel movement
- I have had a dull ache in my left side off and on since
- I stress easily and have health anxiety
- My father passed away on December 8th after a long battle with Leukemia, no doubt increasing my stress these past few months
- I have been eating a ton of chocolate and other junk over the holidays
- I had to strain again on January 1st
- I currently feel like my bowel movement isn't complete when I finish
- My stools are currently thinner than 'normal'
- I have alternated between normal bowel movements and thin bowel movements for years, but was told by a doctor in 2006 to not worry about the thinning as it isn't all of the time, and due to my age.
- My bowels are a normal colour
- I do not have any blood in my stool
- I have no weight loss

So..with all of that..does it sound like IBS? (I often get sick stomach and loose stools when really nervous or stressed about something), Pulled muscle (since I can pinpoint the night where I first felt pain there), or should I be panicking like I currently am about it being something more serious?

Thanks!