I've been doing a lot of research on this lately, and here's some of the stuff I've gathered. If you have chronic yeast infections, you should get tested for diabetes - yeast loves sugar and breeds easily in a high sugar environment.
In general, look into your diet... try cutting down on refined sugars (soda, candy, store bought fruit juice) and alcohol especially. Drink a lot of water, and drink unsweetened cranberry juice. yeast doesn't thrive in acidic environments. I've also read some that the vagina can become less acidic after sex and also during menstruation, so increasing the acidity may be your best bet since it started when you started having sex with your boyfriend.
Try taking acidophilus pills.. acidophilus is the good bacteria that lives in your vagina and intestinal tract. It releases hydrogen peroxide, which keeps the yeast population down. You can also use the pills as a suppository.
Also, yeast can become resistant to anti-fungal medications. So if you've found Monistat is just not helping you anymore, you may want to look into home remedies like yogurt, garlic suppositories, tea tree oil, boric acid, and a few others that you can find information on if you look online.
Also look into your hygiene. Wear 100% cotton panties, and don't wear underpants to bed. If you go swimming or exercise, shower and put on clean, dry clothes soon after. If you must wear pantyhose, make sure they have a cotton crotch. Don't use chemical douches; your vagina can clean itself. Use water, not perfumed soap, to clean the area around your vagina. Use a hair dryer on a cool setting to dry the area after a shower. Basically the philosophy is keep yourself clean, dry, and chemical free around there.
But first, see a doctor and make sure you don't have an underlying problem. Then try some of this stuff. If you want more details on the home remedy treatments, just ask or do some further research. There are a lot of detailed sites explaining how to use each of the things I've listed.