Possibly. It could also be something you ate, the digestion system, or one out of a hundred reasons or a combination of all of them.
Gas
some sort of std such as siphilous in your stomach lining
obesity.
gas.
pregnancy, ongoing indigestion, stomach irritation, stomach flu, motion sickness or vertigo (problems with inner ear that cause dizziness and nausea).
If you are actually meaning your stomach, it's probably heartburn. If it's constant, it might be an ulcer, so get that checked out. If you're using the word "stomach" to mean anything in the abdominal area, it could be anything.
Yes, it happens all the time that women can have symptoms that they believe are due to pregnancy, when there is another cause. If you think you might be pregnant, take a pregnancy test.
if you did well than yes
Vicodin cannot cause acid in the stomach because acid is already naturally inside the stomach but the over use of the Vicodin could cause you to get sick so if you have not eaten then you would be throwing up acid from your stomach which could lead you to think that it could cause stomach acid.
There are many things that can cause a person to feel nauseous. Pregnancy is one common cause. An upset stomach from something a person ate could make them feel that way. Motion sickness is another cause.
If your stomach is growing and you have negative pregnancy tests, you need to see a physician. This could be a result of a benign mass (cyst), an infection, or any other number of things that could be harmful in the long run if ignored. You shouldn't feel movement in your abdomen early during the pregnancy.
The symptoms you describe are not ones that could be put down to pregnancy especially at this stage of your cycle. There must be another cause.