Brovo's advice is pretty valid actually. :) It is possible that you might be getting tired to RP without realizing it. If that is the case, then some time off the RP could do wonder for you. 

Another thing that I think you can do, if you're really wanting to RP but unable to do so in forum at the moment, try a chat RP. It has the drawback that you have to manually save your work (the RP chat) and short posts, but it is faster since your RP partner is online with you. 
I did the same thing with Hikari back then. We both wanted faster response and got tired of having to refresh the topic every other minute, trying to see if there's a new post in our RP, so we started to continue our RP via messenger and saved it, then upload the saved convo to the forum as a 1 big post each time.

Hope that can help. :)