How early do pregnancy symptoms start?

I am possibly pregnant. If so, it has been 18 days since conception. The first “symptom” I noticed was that my nipples and breast were very sensitive. This happened within the first week…I would say around day 4-5. Around the beginning of week two,I started to feel nausea but not “morning”…off and on in waves all day.This is still happening as I type this. I have also noticed headaches,more frequent urination,spotting,some cramps,constipation,increased gas,and have been very tired over the last week.The thing is that I have had bad menstrual problems for years and very irregular bleeding. Inspite of these symptoms, I am a bit in denial. I never thought that I could get pregnant. I have no insurance and have never been officially diagnosed with a condition but have the symptoms of pcos.This seems very impossible to me but these symptoms have me thinking otherwise. Possibly concieved on April 5,2008. Today is April 23. The problem is that I have no way to say “ I missed a period” because mine are not nor have they been regular in years. That is not reliable for me. Just have symptoms to go on right now. I am taking it that a home pregnancy test isn’t really reliable until atleast 28 days from conception.