My experience
Well, of course it is always a good idea with weight training to take breaks between working specific body areas. Everyone will tell you that and the whole bodybuilding industry has been built around it. Good policy.
However, one thing I have learned recently is that my biggest problem in the past with reaching my goals has been stopping EVERYTIME something was sore or achey. After talking to so many weight loss winners and success stories, they all told me the exact same thing. No Pain, No Gain. Really. If a person expects weight loss and fitness to come painlessly they are in for a big suprise. It should be so easy..... But it aint.
The truly successful people I have seen here online and in real life all say pain is part of the process and you need to simply work past it and through it. When I first started out in earnest my back would KILL me after a 20 minute walk. The advice I got from my overweight friends and family, take a few days off. Then it would kill me again, and a few days off, pain again, time off, etc. Long story short I reduced the amount of overall pain, but I was NOT losing weight or getting closer to my goals. Then I started talking to people who told me pain and aching is part of the process, so I started pushing past the shin splints and backaches, and kept walking. Soon that 20 minute walk that had been hurting me for 3 months (on and off with the breaks) wasnt painful in the slightest, even though I had walked every day that week. Then I upped it to 30 minutes, then 40, then 2 hours, then running, etc. I did not stop everytime it hurt, I just pushed through it and kept going, and it went away. Magic! Now 61 pounds lighter (for the first time ever as an adult) I can run further than I ever thought I could walk, and it doesnt hurt at all!!
The same thing happens in the gym. After a long period of inactivity you can be damn sure that your first workout, even though much smaller than your previous accomplishments, IS GOING TO HURT!!! If it doesn't you aren't doing something right! 5kg is a lot of weight if the only thing you lifted for 3 months before that was a pencil, regardless of how much you used to lift. Part of the process. But you can bet your bottom dollar it wont hurt so much in a week.
But take it slow. The last thing you want to do is hurt yourself and cause an injury which will force you to take a break. But if it is just stiffness and soreness, get some muscle rub, try to get some sympathy massages (preferably from someone cute) and ride it out. Don't stop for a week because it is sore, otherwise the next week you will be sore again, and again, etc.
To me it is the same as when I worked on the contstruction site and I asked my boss if I needed gloves. He said its up to you. If you wear gloves you wont get big painful blisters and calluses on your hands. But every time you forget or lose your gloves, you will suffer the next day big time. Or, you can take the suffering up front, build the calluses and hardness in your hands for the first week. Your hands will hurt like hell the first week, but they will never hurt again, whether you bring your gloves or not. I tried both ways, and trust me, it was worth working through the pain first and not suffering later.
Running for me was the same way. I suffered at first driving my 260 pound frame to lengths it had never gone before. And it hurt like hell. But if I took time off everytime I was sore I would still be running only 1 day a week and whining the other 6 about how sore I was. Instead I run 5-6 days a week now and feel freaking great! Pushing past the discomfort made all the difference. It doesn't make me more manly, just stronger and fitter and ready for anything to come.
I hope that helps.
sirant