There are a lot of things to factor in when TTC. First you should know that even couples that are completely healthy can take 1-2 years to conceive. Just because a family member did without problems doesn't mean you'll be the same. (Even if it's a twin) Do you have regular cycles? If not, that would make it harder to know when you're ovulating. If they are regular, you could track when you're ovulating using charts online. If they're not, you can use OPKs. They help to track when you ovulate. (I've personally never used them so I can't say much else about them) Also, if you're using any lubricants, that might have an effect. A lot of them can have a negative effect on sperm and can make it more difficult to conceive. The only one that's "sperm friendly" is something called Pre-Seed.
Have you been tracking when you ovulate? It's a total myth that all women ovulate on day 14...knowing when you ovulate is the first step towards baby making. If you haven't done so already, start a bbt chart, and chart you basal body temperature as well as cervical mucous. After a couple of cycles, you should be able to know when you ovulate and time BD accordingly. If you are looking for natural boosts, there are women that swear by acupuncture, vitex, soy, and other herbal supplements (I'm actually on EstroSense right now hoping this will do the trick!) You just have to find what you believe is best for you!
BTW, are you on prenatals yet? A lack of certain vitamins / minerals can also be a reason for a lack of pregnancy, and the vitamins (especially the folic acid) will help the fetus and protect it against neural tube defects once you do get pregnant.
Hope some of this will help you! Sending baby dust your way :)
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