Signs of Pregnancy

I am wondering what signs there are that you are pregnant before doing a pregnancy test. I did an ovulation kit about a week ago to find out when i ovulate because my cycles have been irregular. It is like a pregnancy test as in when you have 2 lines on the test it means you have an LH surge and are either ovulating or within a few days you will ovulate. Well my husband have had sex regularly for the last week. My question is what are some signs i may be pregnant before I take the pregnancy test. With my son i had no signs i was pregnant until i missed my cycle or if i had symptoms i never realized it. Today i have been nauseous, had tailbone pressure, really low abdominal cramping. I know that I am at least a week and a half away from my cycle. Any advice would be great. I also would like to know if anyone can tell me how soon before a missed cycle i can do a pregnancy test.