Could i be pregnant or its just my mind playing me as i have been ttc for a long time?

hi everyone,my last period was on 17th may to 21st may,since february my period has been coming every 18 days ,before that my period had been irregular but my gp put me on pills in february to regulate my period and it has been coming every 18 days,i have been trying to conceive for long,4 days after my last period i have an ovulation test and it was positive,so i had plenty of sex :).,,so if i was expecting my period again after 18 days ,i would be am 3 weeks late for my period,i did a preg test in the morning today but was neg,i want to know if i might be pregnant,and that the test didnt detect it yet,how long i should wait to make a test and if i go for a blood test now if it would show for sure or it might still be neg-,,i have been having very bad headache and cramps,and i feel a bit bloated and have been nauseous for a week but didnt throw up,i was pregnant 4 years ago but miscarried on 5 month,my first pregnancy i didnt even know that i was pregnant before 4 weeks but this time i cant wait ,am just too eager to know,any advice thanks,,,am 23 ,5 years married no kids yet