I thought this was going to be an herbal remedy issue, but clearly is not. Seems to me you might be thinking of guilt when you try the spells. If you are, or were, in a Christian home, I can understand. You are getting nervous about this nagick, and causing your own belly ache. Sounds weird, but I know people who can make them selves sick to get out of doing something or to not have to go somewhere. This could be happening to you, only you are doing it over nervousness of doing spells.
Since you said you are starting, you need to learn and apply the basics of magick.
Here are some links to help you:
http://www.spellsofmagic.com/read_post.html?post=71692-Starrie's "Starting Out" post
http://www.spellsofmagic.com/read_post.html?post=483942-AwakeTooLong's "Basics: Expanded" post
http://www.spellsofmagic.com/read_post.html?post=251089-Basics by Sagesk
Also about.com is a good site for all kinds of info. Once there, put Wicca basics in the search bar. It will take you to basics of magick, too. I was on it for hours just looking and reading. And copy and pasted a lot of things to my computer.
Blessings!
First of all you need to visit your doctor in order to establish what is the physical reason, if any ,behind the pain that you feel.
Have a very close look on your nutritional habits.
Ask your doctor to test you for the presence of Helicobacter pylori.It is bacteria ,which eventually creates ulcers into the stomach lining.It also can cause gastritis and has been linked even with cancer within the area.Some viruses such retrovirus ,Norovirus ,Adenovirus and Astravirus can trigger gastroenteritis.
Start eating smaller portions every 2 or 3 hours ,instead of having big meal after 4 or 5 hours.
If your doctor agrees and you do not get medicines that can interfere with, you can drink oregano tea.
In case that it is stress related ,try meditation or any type of moving meditation such Tai Chi.
Only then try casting any spells as additional help.
Oh, and one more thing. Doing meditation before spellwork might make you more calm, less nervous and no belly ache. Also, if this is not right in your mind or belief to do magick, then I recommend thinking on the path you really want for yourself.
Blessed Be...
Are you sure you don't have some anxiety or fear over practicing magick? Tummy trouble is a sure sign of nerves.
Try to meditate and relax, find a calmness within yourself, ground and center before ritual. Keep it simple. It's best to start off with rituals and spells that do nothing more than cleanse and protect you. Do the same cleansing and protection spell everyday until it becomes a normal routine you feel comfortable and confidant in. Once you are capable of this, you can move forward.