If you have parasites in your body it could be as a result of weakened immune system from heavey metals or toxic chemical exposure. You might kill them but its easy enough to be reinfected so its important to build up your immune system.
If you have ever had metal fillings it is likely that you are overloaded with heavy metal mercury poisoning.
Consider having a hair mineral analysis for basic heavy metals and minerals. They are relatively cheap - should be approx $80. Its an good indicator of mineral imbalances and heavy metals, though not conclusive it gives you an clearer picture of whats going on in your body.
Then after you could buy a couple of home test kits for mercury or heavy metals.
1) do a urine sample first to see mercury and heavy metals.
2) (WARNING: dont do this if you still have mercury fillings or have just had them removed. Wait 3 months first) take alpha lipoic acid 60mg approx every 3 hrs during the day and night and then in the morning take another urine sample and see if the urine sample shows more heavy metals or mercury. If it does then you know you can try taking alpha lipoic acid for a while to help chelate it all out.
(WARNING: dont do this if you still have mercury fillings or have just had them removed. Wait 3 months first)
Or pay for a DMSA urine challenge test. Much more expensive but will be more accurate in determining whether or not you do in fact have heavy metal poisons in your body.