weight training plateau??????

Give yourself some proper rest. If your muscles are feeling tight and tight, that is a huge indicator you need to rest. Also, muscle definition takes time. You saw at the beginning a big difference because your body wasn't used to the exercise. You are tense and probably looking pretty buff now compared to before. Sounds like you are doing a fantastic job with your crossfit routine. I also do the same kind of workouts. If rest isn't the case (You are properly working out 3 days a week) then maybe its your diet. What kind of diet are you currently doing? If you are not in taking enough calories your body will not be able to grow. That is why you hear commonly; Bulk then Cut. Very hard to do at the same time. Maybe add some protein after your workouts and in the AM on days you don't. Just my .02

Have you been doing the same routine or different routines? If you've just been doing say, the workout of the day and various things everyday...maybe you should start an actual routine and stick with it for about a month. Or, if you're on a routine, try incorporating different things. When I get stuck with my strength routine, I try to just stick with the core moves I know are working and add a couple reps and then alternate body parts. Right now I do Shape's Ab Solution every other day, and I alternate arms and legs, so on arms day I mostly just lift weights for my arms and do some cardio. On legs, I do 8 Minutes to Slim which is an all-over body circuit but works mostly your abs and legs, and I do plie squats along with some other leg moves. Maybe you should try this?