Hello, Mr. Deepak,
Masturbate from last 15 years,
Penis size when full in erection is varies from 10 cm to 15 cm. ( few exception is there).
Girth is 1" or slightly more 1 1/4" at the time of erection.
More or less in your case your penis is normal so don't worry about that.,
Semen is usually thick with creamy whitish color with shining.
Semen amount ( quantity) is 2-5 ml ,so normal .
Sperm count ,you mentioned that it is 15 % ,but not clear what is meant by this.
Sperm count is normally 60-120 millions.
Back pain not related to this problem.
Now most important question is
erectile dysfunction and
premature ejaculation.
For these two problems , you should
consult a psychiatrist and result will come out within 2-3 days as you like.
Don't trust over QUACKS.
Hope I have answered your query.
If further any question I will help.
GOOD WISHES.
Dr. HET