Forget about the gastroenterologist. Most of them have no idea what a candida overgrowth is, and will also tell you that you may have
parasites only if you visited a tropical country. If you dare talking to them about candida or parasites, they will take you for a hypochondriac. I've been there.
I'm sorry to say, but it will take far more than that to heal your gut and resolve your issues.
First, how is your diet? You can't heal a gut with a standard american diet. You don't have necessarily to go extreme (anti-candida diet) if your case is not too severe, but a good diet is key. I suggest a lot of raw vegetables, fruits in moderate amounts on empty stomach, good oils (coconut, olive, pumpkin seed), and animal proteins in reasonnable amounts. Improving digestion is key in this battle. Learn about food combining.
Next comes the candida killing. If you're 18, you're probably dependant on your parents financially. I suggest cheap but effective antifungals: raw garlic, turmeric, oregano essential oil, coconut oil. Rotate them every week at the most.
When you target the candida, it will die and release even more toxins. You want to take care of your liver when you do that. Try to get your hands on some milk thistle. Also, I suggest you consider liver flushes.
About your solution: colostrum is a great supplement for gut and candida issues, but I feel that one capsule is a far too low dosage. If you are in the US, iherb.com sells a great colostrum powder by Symbiotics (21 oz). I as taking 6 grams a day at my worse.
Also Bacillus coagulans has been proven to be effective against candida. How many billions you have per capsule?
Glutamine is not needed and may be even counterproductive due to ammonia issues.
I suggest that you also start making homemade kefir. It is a cheap probiotic drink, and work wonders for candida and parasites.
There are other measures you can take to heal, but this is already a good start.