I just noticed your post, sorry for not responding earlier. My interpretation of a nervous stomach is that you have a head/gut reaction when in an anxiety state. In other-words, when you are anxious, your gut immediately reacts. You may get stomach pains or have diarrhea, or a feeling of urgency to go to the bathroom or there may be some other gut reaction when you are anxious.
Remeron is meant to be taken on a daily basis. I wouldn't mess with taking it as needed. Your doctor should have explained that to you and 7.5 mg. is a very low dose, so I wouldn't worry about it especially if it is doing the trick and keeping you from having gut problems. The great thing about remeron is that it can kill two birds with one stone. It is an antidepressant, but it sounds like you doctor is prescribing it to you for anxiety (which it has been know to be effective for) and the bonus is that it can make some people constipated (not us because we have diarrhea therefore normal bowel movements). For people like us that translates into having a normal bowel reaction instead of constant diarrhea or urgency. Your doctor wouldn't have prescribed this to you if you had predominantly constipation as it is know for slowing down the digestive system therefore making it a nice medication for those of us who have issues with diarrhea. Oh, I forgot to mention the other advantage and this is a biggie, sleep. It really helps with sleep at night. So in fact, for some people it kills 4 birds with one stone (antidepressant, anti anxiety, constipating therefore making some people more regular because they normally have diarrhea, and sleep). Kind of a great drug for some people. Everyone is different though and it isn't for everyone, but if it is helping you, I wouldn't second guess it. Sounds like your doctor is pretty well informed.