Strange sleep cycle

I'm 17weeks now and finding it increasingly difficult to get enough sleep. I wake up early (6am, sometimes earlier) before alarm rings, and cant go back to sleep anymore. I usually feel tired after lunch and try to end work (office job) early to catch a nap around 5pm. I worry this might affect my job performance. Any advice from the mummies here on how to get better sleep and how to juggle with work? #1stimemom