Firstly, welcome to the wonderful world of Aikido!!
I too am a relative newbie (4.5 months now!)who had done almost no real exercise and my instructors recommended a hot bath after the lesson to help warm the muscles and loosen them again.
Good thing is though, that the more you practice the less the aches get you!!
I think after 3 or 4 weeks my aches didn't seem noticeable the day or so after!!