If it comes and goes during the day, it is probably just tensed areas of muscle tissue. Stress/anxiety can make you think you have everything under the sun. An infection, especially when lymph nodes are concerned, seldom comes and goes during the day.
Hey, I think I know what might be wrong. Actually, yesterday I was looking online because I have/had swollen lymph nodes and tired/weak legs as well and I went to the doctor today. Well, first of all, I have to ask you: Do you have ANY type of pimple-looking things/sores on you anywhere on your body? Like any type of sours that just look like normal pimples, besides on your face? If so, then it's most likely herpes that is causing your lymph nodes to swell up and for you to have weak and tired legs. (Don't even have to have the sores and you could still have herpes, see below) That's exactly what I found out today. The doctor told me that the tiredness in my legs is the result of the infection (herpes) that is affecting the nerve cells in my body. Herpes is a virus that lies dormant on the nerve endings in the spinal cord and when something triggers the virus to express itself (and there are a million things that could trigger the virus to actually affect you, i.e. stress, depression, being unhealthy, etc...) then it spreads itself out to other nerves in your body (especially the legs) and so that's why you're feeling that with your legs. It's not going to damage anything or be detrimental, so don't get freaked out. The swollen lymph nodes are also a direct result of the virus. Your body is catching, trapping and attempting to destroy the virus in the lymph nodes and so they become enlarged/inflamed because of the virus which your body cannot completely kill (Herpes, as you may know, is incurable). So, what you have to ask yourself now is; have you ever had tingling anywhere on your butt or groin area? My doctor said that the tingling sensation is also a sign of herpes- when you actually notice it and it's not just a once in a blue-moon tingle. It is very possible for someone to have herpes and never know it, as everyone's body responses differently, i.e. a lot of people never even have any kind of outbreak, but still have herpes and can still transmit it just as easily through skin-to-skin contact!!!!!
So, hopefully, I've been able to help you somewhat or at least give you a suggestion to give to your doctor that maybe you should have a blood-test done to check for herpes.