I think this is normal. I know I definitely go through stages, sometimes I feel like what I've written is pretty good, then other times I feel like it is total dreck.
A while ago I actually quit writing after trying my hand at short stories. I wrote a bunch of stories and subed them to pro-paying venues. Form rejections from all of them...so I thought, well I must just suck. But then, a few stories I wrote got personal rejections including a very encouraging one from the tor.com folks. I credit that personal rejection with why I kept writing, eventually I sold a story and get almost all personal rejections now. Figure the next step is to sell more stories (I hope)
My point being that you might actually kind of suck. I definitely did and still do a lot of the time, but I kept plugging away and the practice actually helped me get better. Sucking is totally ok!
Reminds me of one of my favorite quotes from Ira Glass (not that I assume you're a beginning writer necessarily, but I do think this is just so encouraging in those moments of self doubt):
“What nobody tells people who are beginners — and I really wish someone had told this to me . . . is that all of us who do creative work, we get into it because we have good taste. But there is this gap. For the first couple years you make stuff, and it’s just not that good. It’s trying to be good, it has potential, but it’s not. But your taste, the thing that got you into the game, is still killer. And your taste is why your work disappoints you. A lot of people never get past this phase. They quit. Most people I know who do interesting, creative work went through years of this. We know our work doesn’t have this special thing that we want it to have. We all go through this. And if you are just starting out or you are still in this phase, you gotta know it’s normal and the most important thing you can do is do a lot of work. Put yourself on a deadline so that every week you will finish one story. It is only by going through a volume of work that you will close that gap, and your work will be as good as your ambitions. And I took longer to figure out how to do this than anyone I’ve ever met. It’s gonna take awhile. It’s normal to take awhile. You’ve just gotta fight your way through.”