Why even go to the doctor if you're not going to follow his advice? Talk about your medicine phobia with the doctor instead of just going home and ignoring the prescription amount.
Taking half the dose will not give you the same affect that taking the whole dose will. He prescribed 50 mg for a reason. No amount of reading that you can do will give you the same level of knowledge and expertise that your doctor has.
The other factor that affects the results of taking medicine is the length of time you've taken it. I've taken several different psych meds and the doctor always tells me to not expect to notice a difference for anywhere between 2 and 4 weeks. I don't remember the length of time for zoloft.
I've taken zoloft and it has been effective. I don't remember the dosage. I do know that your doctor prescribed 50 mg and expected you to take that amount. You cannot know if Zoloft is going to help you or not until you take the correct dosage for the length of time needed before it builds up in your system and thus becomes effective.
I urge you to call your doctor and tell him what you've done. He will either tell you to take the 50 mg. or will suggest a different medication. Follow his advice! Give meds a chance.
I, too, have anxiety issues. I've been so seriously anxious I had difficulty driving or taking care of day to day business. So, I know that this is not easy for you. I urge you to make yourself trust the doctor and try what he suggests. The worst that can happen is the medication won't help. Side affects are temporary and short lived once you're off the medication.
It might help for you to make a list of the reasons you are phobic about medicine and discuss those reasons with your doctor.