There is (for once) a fairly good explanation of hair loss on wikipedia, but briefly it is caused by a byproduct of testosterone, called DHT. DHT is created in the body when testosterone reacts 5alphaReductase, another bodily chemical. The propacea you are using works by inhibiting the production of 5alphaReductase, therefore reducing the presence of DHT. DHT "attacks" hair folicules, resulting in thinner hairs (colloquially known as peachfuz), which in time fall out and are not replaced with a new follicule. It should be noted however that all people lose about 50-100 hairs daily, and so you need not panic if you notice a lot of hair in the shower, for example.

Consider using monoxidil. unlike propacea (anti 5αR), and nizoral (anti-androgen, testosterone/DHT killer), monoxidil is a growth stimulant which can cause hairs to regrow. It's not as expensive as it used to be either. Nizoral is affordable and works well in conjunction with monoxidil.

From a dietry perspective, remember that most of your hair is protein, and so get plenty of high quality lean proteins in the diet (saturated fats raise testosterone and so don't eat red meat more than a couple of times a week). plenty of chicken, turkey, soy proteins, egg, nuts, seeds and pulses.

Other important nutrients for hair are:

silica: found in potato skin, apple skin, bell peppers, tomato, grapes.

Zinc: found in turkey, beef, walnuts, pistachios, green and black tea.

Iron: Found in red meats (but as mentioned above, don't overdo it) such as beef, horsemeat (if you'll eat it), also liver, lentils, some other pulses and some nuts.

Consider taking a multivitamin also (not instead of) the above. Do not take a multivitamin with tea or coffee, have it with lunch instead of breakfast if necessary.

Liquorice, peppermint tea, chammomile and saw palmetto have all demonstrated 5αR lowering properties. Infact, saw palmetto is used by some as a natural alternative to propacea. If you are ussng, or considering using propacea, consider saw palmetto as an alternative. Try to get a fix of many as the above (in their purest state, pure liquorice candies will have some effect, liquorice allsorts, which contain less than 10% liquorice, which will do nothing).

Black tea has been shown to reduce dht (most of the good press goes to green tea). However, if you are american, powdered tea/bottled ice tea/cheap shit tea does not count. Buy good quality English blended, or Indian/Asian black teas. If you are British/Australian, remember that the addition of milk significantly reduces the effect. If you can't drink it black, go for a strong brew with less milk.
Curiously, green tea actually seems to slightly increase dht (it is not clearly understood how, nor how black tea lowers it). However, given the enormous health benefits of green tea that are much less in black tea (more antioxidants and cancer killers than a whole broccoli and two carrots in one cup, reduce cholesterol, fat burning if drunk before exercise, anti ageing, anti hair greying/whitening etc), i would still suggest a cup or two of green tea a day also.