I've looked at the Dr. Natura website and it appears that the main ingredients are psyllium husks and flax seeds. Both of these (especially the psyllium) can be very irritating for people with IBS. I was amazed to see that they actually tout this product as being good for IBS (it also has some other fairly strong herbs in it). I DO take a little psyllium if I'm really C, but I have to be very careful with it as it can cause bloating and gas if I take too much. Flax seeds are very nutritious and high in calories (hence the 42 calories per dose of Dr. Natura). However, flax oxidizes very quickly (goes rancid) once it is ground, so it's best to grind whole seeds in a coffee mill each time you take it.
I'm sorry to hear you've had so much grief since you tried this supplement. In my experience "gently does it" is best to avoid IBS-C symptoms. The best thing I've found is to start the day with a big bowl of oatmeal (not the instant kind) with some soft canned fruit. This seems to give my tummy a "buffer" to absorb whatever else I eat. I also follow Heather's advice to always start eating the soluble fiber food first at each meal. For example, if I have yam, white rice or potato with chicken or fish, I eat the yam, etc. first. Everyone has different trigger foods, so it's good to keep a food diary and try to see whether certain foods cause problems.