Some people have soft, mushy sort of poops all the time; it's normal for them. If this is a departure from your normal poops, then yes, it can be a sign of IBS symptoms. If it stays like this for a long time, though, it may be your new normal.
Have you added any new medications--including vitamins or supplements or protein powders--since this started? Many medicines will affect your bowel movements. Sometimes your body adjusts, and sometimes you just have to redefine what's normal.
Also, look at your diet. Have you added anything new lately? A glass of fruit juice for breakfast? A salad every day with lunch? A coke in the afternoons to perk you up? It doesn't take a lot to make that kind of change. Even just taking something you are okay with--fruit juice before bed--and moving when you consume it--fruit juice for breakfast--can change your bowels. Or consuming too much of something or consuming it too often. I'm okay having some Kool-Aid, but I can't have lots of it day in and day out; either the fake sugar or the acid in the Kool-Aid, or the Vitamin C (or all of them) will start making me have D.
While soft, mushy poop can be considered D, with only having one poop a day, I don't think a doctor will see that as D. If, however, you feel the need to go to the bathroom, but have no stool (what I call a phantom poop), that can be a form of D. Otherwise, needing to rush to the bathroom and having an explosive bowel movement is just IBS and isn't D, per say. Even if your stool was perfectly normal, the need to rush and the explosiveness of it would probably indicate IBS. Some people have poops that fall within the "normal" range, but still have IBS symptoms, which not only can include the rushing and the exploding, but gas, cramping, and an inability to tolerate a number of foods (and a few other things I'm probably forgetting).