I lost my pregnancy on January this year since then I have tried getting pregnant in vain.what can be the problem

It takes the average couple a year or more to conceive once they actively start trying. Miscarriage is common, sadly. Did you see a doctor after the miscarriage? Did you have a full physical done to determine why you miscarried, and if there's an actual problem? Are you tracking ovulation and having sex during your most fertile times (don't use an app to track ovulation, the best way to track is by using basal temperature readings daily, and it can take 6 months to a year to accurately track ovulation with this method, which is the most reliable method to track ovulation).

I wish we could tell you why you aren't conceiving, but it's not possible to determine that online. It could be something serious, it could be nothing at all, just bad timing. To get an accurate reply you'd have to see your doctor.