Oxandrolone is one of 'safer' orals and keep in mind it is primarily (one of the few) metabolized by your kidneys. If you are urinating more go to a pharmacy and buy a chem 10 or chem 12 urinalysis strip. Read the protein, specific gravity, and PH balance. If the colours change your urine could be too concentrated or the opposite. I find it harder on the liver and chemstrips have a few 'decent' liver tests as well, but a chemstrips test can't hold a candle to blood work.
Just a gauge to use weekly - which I do as 100 strips are not a lot of money.
I agree with
@gondar1 - if you are new, I would stick with one test ester and get used to normal injection protocols as sustanon has multiple esters plus you are using Test C. NPP is a nice compound, but hard to give you advice without proper blood work. Pay a Naturopath to get a CBC, lipids, liver, kidney, inflammation markers, etc. done. Again, if you are new - this info is invaluable for the future. If not having joint pain I would just stick with test and if you really want to add in 40 mg of Oxandrolone so be it.
You should expect strength gains, doesn't covert so lean muscle growth but nothing compared to other orals. Before I had to give up orals - it was a favourite as I did not want to be huge but loved being leaner and stronger (no water retention).
Are you up urinating at night more often? It should not make you urinate more unless something else is going on. You can get a jug with a marker and look up average amount of urine per person per day - of course if depend how much you drink, but if you don't change anything - take a leak in the container for 24 hours and then you will know for sure.
At one time I had to go back and buy another container as I was urinating twice as much as I should - no PED reasons and the docs never figured out why, but after I knew I was going to much, I was sent to a urologist who did a 24 hour urinalysis - two kids: One for carninoid tumours (they look for 5=HIAA) and one for protein/other urine markers to indicate something was off. If you ever go down this road, read the paper they give you as many medications and even foods can increase the markers and indicate you have a carcinoid tumour. I did a second one after reading the insert and was negative.
I am going deep on this and don't want to make you paranoid, but good noticing changes. Your body talks to you and you should listen. If it is a significant change - then investigate.
Best of luck!