hello concerned 20 year old,first of all relax and understand
masturbation is a natural sexual urge that happens to almost everyone as a part of their "growing up process".
You should be concerned only if it is in excess and affects your daily routine-studies/job or personal life or social life.then that is a concern.
pain in your lower back is not at all directly linked to masturbation ,chances are you have strained your lower back or you have a case of mild
dehydration and small
kidney stones.i would suggest giving more history details to assess the same.
In the mean while ,i would suggest you to do the following,
1)relax and practise meditation
2)cut down on masturbation for a while,meaning lower the frequency and distract yourselves with other activities and spending time with family and friends .
3)take a
multivitamin tablet daily for 2 weeks,have 2 litres of water everyday and meals at proper timings
4)apply warm cloth presses on your lower back and apply
diclofenac gel for pain relief twice or thrice daily.
try this and i believe you will be alright within 3to4 days.
hope i have clarified your concern and good day.