yes I definitely feel this way as well. Thats why Ive been challenging myself with this #HiveBloPoMo to get 'over the hump' of creating loose form content. Getting comfortable with freewriting basically... otherwise I just over think the blogging and end up doing nothing because i feel overly pressured by my own sense of perfectionism.
My advice: Start by creating some total dross that you dont need to feel proud of, and do it a bit every day or a few times a week, then you'll start to find that some interesting subject matter comes up and its not so hard to figure out what to say! maybe.... I dont know, its just what Im trying for myself anyway!