Yes, it could be IBS, but sometimes people get a bit free with that diagnosis. Having gas and related gas pains is normal. Having a bowel movement twice in one day is quite normal for a lot of people. When normal becomes abnormal is when it really starts to interfere with your life. When pain is unbearable, when you bloat to the point you can't wear your clothing or even look pregnant, when even your one or two bowel movements a day are hard to pass or hurt or have a lot of mucus with them, even if they look normal.
Since you're a vegetarian, I daresay you eat lots of veggies. Veggies, especially in their raw or al dente state, are bad to cause normal people gas. Beans too, obviously, cause a lot of people gas. Raw fruits and fruit juice can cause gas in some people (apples seem to be universally the worst offender).
Have you been able to combat the gas with OTC gas relievers? Have you tried keeping a food diary to see if one or a few things in particular (e.g. beans or raw broccoli) makes it worse? If your problems are mild and controllable with diet modifications and/or OTC stuff, then you are within the realm of normal.
Have you ever had a colonoscopy? If not, and given your age, make your doctor convert that sig to a full colonoscopy. A sig only looks at the lower part of the large intestine, while the colonoscopy goes much further up into it. A colonscopy is recommend for people over 40 every 10 years to look for colon cancer.
That your doctor wants to do a sig is a bit weird to me (based just on what you've described as symptoms); it looks at so little of the intestines, what's the point in your case? He's not going to find the cause of your gas problem in such a short amount of space. They're usually used, as I understand it, for people with lower-intesinal problems, such as when the doctor suspects hemmroids, skin tags, anal fissures and other things like that that might be causing pain or bleeding right near the rectum. If you don't have those complaints, I don't see the point at all, although if you've not had a colonscopy in the last 10 years, you need one of those just as routine maintenance, as it were.