Strange spikes and drops in sales and position.

I’ve been at this in earnest for about 4 months now and every time I feel I am gaining momentum something happens and I get knocked down. My product will spike in ranking and drop off. It’s really odd this past week I felt I finally had my ducks in a row and sure enough I instantly got my sales but a few days later zero sales and free fall in position for what seems to be it’s lowest since launch. To add insult to injury I have a hijacker that has been keeping me from listing at my regular price. I’d like to believe that I have been learning a lot but I’d be lying if I didn’t feel defeated. Either I really can’t get a grasp of Amazon or what. This time I have ZERO idea what the issue could be now.