Is it common not to get any side effects from Finasteride after a week?

Thank you for your question. You are asking if it is common to not have any side effects after being on finasteride for a week. You add you have been getting conflicting information about side effects being common and not common.  
I can help guide with you with this, even without a physical exam and more details about your hair loss situation. I’m Dr. Amiya Prasad. I’m a Board Certified Cosmetic Surgeon and Fellowship Trained Oculoplastic Surgeon. I’ve been in practice in Manhattan and Long Island for over 20 years. I’m the founder of TrichoStem Hair Regeneration Centers, which employ a non-surgical pattern hair loss treatment for men and women using PRP and extracellular matrix since 2011, which pioneered a new classification of hair loss treatment.
Side effects of finasteride are actually very rare, so your reaction so far is what the majority of men on finasteride experience. The incidence of side effects due to finasteride is experienced in about 2% of men taking it. I’ve had patients who were prescribed finasteride in 1998, and still take it today without side effects. Of the few patients I’ve had over the last 20 years who experienced side effects, none of them had it permanently, and were able to restore normal function by stopping the drug.
In my experience, the risk of side effects of finasteride is extremely low. The men who do experience side effects are much more vocal about it than the vast majority of those who don’t have side effects. There are also more common causes of sexual dysfunction such as stress, lack of sleep, and lack of exercise, but it is often easier to blame a drug than one’s lifestyle.
I suggest you keep taking finasteride to slow down your hair thinning. You may want to consider other treatments, as we have had patients both on finasteride and not taking it benefit with thicker growth of thinning hair, and stimulating growth from hair follicles that were not growing with our Hair Regeneration injection treatment. As I mentioned earlier, we have been administering this treatment since 2011, longer than any other practice using the PRP+ACell combination, and treating far more patients with it. It works on a mechanism separate from finasteride, so it does benefit younger patients on finasteride, older male patients not on finasteride, and female pattern hair loss patients as well. Over 99% of pattern hair loss patients are seeing visible, renewed hair growth and denser hair coverage, with most of them getting just one treatment that can last 3-5 years, or beyond.
I suggest you keep taking finasteride, and look into other methods to not just slow hair loss progression, but to increase hair density and coverage for the long-term management of hair loss. I hope you found this information helpful. Thank you for your question.

In my experience, side effect to finasteride are uncommon, in 1 to 2% of patients. So it would not be unusual at all for you to not have side effects,Dr. Robert Jones

Generally speaking about 1 in every 40-50 men get side effects of some kind from finasteride. In my experience, side effects can be reported as early as day 1.