Help!

So after having our baby I wasn’t in the mood for a really long time. We hadn’t had sec since April. We did it the other day and now I’ve been noticing my lower back and both of my legs from top to bottom ache so bad. Even my armpit area hurts on one side. Has anyone else experienced anything like this after not having sex for awhile and then jumping back in. I was on top in a reverse cowgirl position for most of it. Which is something I’ve only done a couple of times in my life lol.