there really could be any number of problems going on here.
Firstly, it's pretty important to admit that 6 months is pretty much no time at all when it comes to learning to play guitar, especially if what you're trying to learn requires a good amount of technical facility. Even if you somehow manage to practice 8 hours a day every day (not advised generally, but even less so for a beginner), it's just not much compared to the process of learning (which never really ends). I've been playing for about 13-14 years now and I constantly feel like I barely scratch the surface of what music has to offer. I wouldn't be so quick to blame having weak anything, because realistically when it comes down to it, brute muscle power is not needed to play the guitar.
Beyond that, it's really impossible to say whether there's something wrong with what you're doing or whether it could be something medical without seeing you play. If you would like we can take a look at what you're doing, but you'll need to take a video and put it on youtube, then post a link here so we can see what you might be getting wrong. They guys above are making some good guesses at what the problem might be, but without seeing you play, that's all they are: guesses.
I would also say, unlike guitarkid8 and dthmtl3, that you should avoid really anchoring. You're early enough in to your learning that if you do already it's easy to fix, and I believe that true anchoring is something to be avoided.
Finally, and I know if you're in a country that doesn't have socialized health care this might be a sticking point, if you believe that you have some condition that means you can't move your hands very easily or if you feel like something is wrong with your health, go to a medical professional and get examined.