In reply to Noo Noo:
OK so first congratulations on finding this sport. Now please let me offer you some first hand advice, because frankly I don't want anyone else suffering the same way I did.
The good thing is you sound quite committed to getting fitter. The bad thing is that (and it's difficult to say tbh) but I get the feeling you're over-doing it. Let's go over a few things - and again this is from personal experience that I've had with training and ensuing injuries, not theoretical stuff.
- Pull-ups: A good exercise but requires the correct posture and technique. Ensure you're doing wide grip pullups focusing on the back, medium grip pullups which engage the traps and chest and chin ups which engage the biceps. Do Not overdo this exercise seriously it is an intense exercise and I would advise you not to do it every day, give your body time to regenerate. Once or twice a week is enough.
- Stamina probably isn't holding you back. As your technique improves you will require less stamina and strength to complete routes/boulders. In climbing technique is basically 90% of the sport, perhaps that last 10% can be down to fitness and conditioning. You'd probably need to be climbing for several years for it to make a massive difference tbh.
At my local bouldering gym, I consider myself to be a fairly fit guy. And yet some people, more overweight than me, not as strong can flash boulders easily that I just can't. And that is their technique and mental commitment to the moves is just better than mine, being fitter would not help me too much.
- Add in push-ups to your off the wall training. Do wide, normal, narrow (diamond push ups) and engage your core and ass. The push-up is an all body exercise and will counteract the pulling exercise of climbing which can lead to over developed pulling muscles.
- Add other exercises as you want, but if you're climbing once or twice a week for 3-4 hours and doing some pull-ups and push-ups that is quite a lot of exercise and you'll need to make sure your body is able to recouperate from that before adding more. Some basic suggests would be squats, lunges, deadlifts and some core work which you can do on the pul-up bar like leg raises.
- Injuries can happen because of repeated stress and strain on muscles/tendons/joints. Particularly in bouldering gyms, repeated jumping onto the mats can take its toll on your knees. Try to climb down rather than jump down. You may not feel it initially but over time your knees will become weaker if you dont recouperate enough.
- Fingerboarding. Try not to do this too much. If you're climbing regularly you shouldnt need to do this. As you progress you might find it useful occasionally if theres a particular route or move you want to work on. But please only do this when you've been climbing a while and have a better idea what you want to do. Same goes for campus boarding. It's a recipe for injury that could set you back months or years.
- Eat well. You mentioned you have Kidney disease. You may want to consult a professional about your diet, since I'm not an expert. But it is really important that you eat lots and mix in plenty of protein and not worry about eating fat or carb - you need this to be healthy. Make sure before a climbing session you've eaten well, either a carb like porridge which is metabolised slowly or carb like fruit such as bananas which will give you the blood sugar you need to keep you climbing. When you're done eat soon after, protein shakes can help, but also snack on things like nuts or other high protein food.
If you notice your muscles aching a day or two after a training session it is because you have not eaten enough to replenish those muscles. Eat well and you won't feel this aching.