Can I use finasteride 1.25 for hair loss while I have varicocele 3rd degree with intermittent pain and normal semen analysis?

This needs an in-person evaluation. I recommend getting a formal evaluation with a hair loss expert to go over your condition and advise you on best treatment options. There are great non-invasive options like prp/progesterone and/or hair transplantation. See an expert. Best, Dr. Emer

It's a great question - but a complex one too. The short answer is you'll want to have a thorough discussion with your urologist.  Some of the factors that influence whether you are given a 'yes' or 'no' answer are your age, previous sperm counts, degree of pain, whether you have children or not, whether you want more children, what treatments you have used for hair loss already. One needs to be aware of the possibility of future reductions in sperm count with both the varicocele and with finasteride.  Having both your urologist and hair loss physician on board with discussions is critical. One can not give a yes or no answer to your question as there are too many factors to consider. 

There are no studies linking increased varicocele pain from finasteride use so you should be fine.  IF you are having pain now, you will likely continue to have pain.  
Good luck!

Taking finasteride in the face of a varicocele and testicular pain may not make it worse if that is what your question is. although some people get testicular pain(rare) from the drug, since you have it now, I do not suspect it will worsen.