I write like that too. I really worried about it during my MA and wrote at length about how planning didn't work for me (and what did) in my portfolio commentary. Fortunately the feedback on this confirmed what I felt - that I was better off sensing my way through than planning in advance. I think that's just how some writers are. I tried to make planning work for me, but couldn't. Now I've no desire to.
If I follow a plan the writing doesn't seem 'alive' - I don't feel so connected to it and I don't think it shows the emotional webs between characters or the main character's emotional journey so well. For me the work progresses and builds on what's come before, so instead of looking at a plan I look back over the chapters I've already written to see where to go next.
Plenty of fantastic writers don't plot/plan in advance. Marilynne Robinson, for example, says she doesn't, that all the action is generated out of character (I think that was in her Paris Review interview, but it could have been from her collection of essay). Henry Green, in his Paris Review interview, said 'write a plan and you'll only depart from it'. I should know of more but I can't think of them at the moment!<Added>
I do now have an 'image' for the end point of both storylines - but I didn't develop even this until I was c.30K words through.
Just remembered, Penelope Fitzgerald was another who didn't plan much - she said to write a novel she needed the title, the opening paragrah and the final paragraph - that was all. <Added>
Ian McEwan said something relevant to this on a recent interview on R4 - but unhelpfully I can't remember what it was.
Btw, if you've any interest in reading my critical commentary on planning vs not planning I'd be happy to share via email