I felt a bit like that at the end of year 1. To combat the dates thing, I made timelines with all the important dates in, and ended up just writing my notes underneath the event on the timeline. I found that this gave me a good, understandable overview of each topic as well as enough details to help me remember stuff! Reading articles and watching documentaries about your topics should also help give you some perspective.
In terms of asking for help, there's no shame in it. I ended up asking my teacher to help me write an example essay paragraph in the first term of Y2 of A levels, and that completely chnged my perspective on history essays as a whole, and took me up by 2 grades. It can be scarey, but your teachers are paid to help you to learn, so as long as you ask nicely I can't see any reason why they'd refuse.
You can do it. I know it feels bad now, but I found Y13 so much better than Y12 in terms of history. Soon you'll have the whole summer to help yourself to understand the topics a bit more, and to have some rest in order to return in September with a fresh mindset.