Im on amoxicillin and ive had weird stool lately, it was dark almost black and one looked like a long parasite. is this normal and should i continue use? im on day 5 its for a sinus infection?

You must continue the antibiotics until complete otherwise you risk having a desensitised bacterial strain. It is quite common for antibiotics to interfere with the normal balance of gut flora and so cause changes in the nature of the stool. It will pass, eat yogourt!

Solid black stool, especially if it is very foul smelling, can be an indication of internal bleeding. If the stool remains black, it should be tested for hidden blood. Do not ignore this. Good luck.