Some may or may not tell a doctor because their doctor may put in their personnal record about using steroids, and insurance carriers look down on it. But getting bloodwork done is a good idea, but you need not a reason when asking for one. BTW, the harm of pills on the liver/kidney is pretty much exagerated online. I have heard they are not much worse than aspirin, so just be smart with it.
As long as you eat to maintain your mass, you shouldnt lose much of you gains. Granted if you use anabolics that increase
water retention, you will lose weight but not necessarily mass when coming off.
You do have to shoot into the muscle. Sub-q injections take longer for the drug to enter the system.