am i pregnant or not

hi, i want to ask something, i slept with my boyfriend without using a condom and i’m also not on family planning so after i slept with him i drank a lot of water, i slept with him on sunday and then on the next sunday i started menstruating, my periods were normal even worse than before but in the last week i’ve experience some symptoms i don’t know if is it because i’m scared or i’m pregnant, i always go to the toilet after 5 minutes and i’m feeling nausea all the time, i’m not ready to be a mother yet could it be that i’m pregnant and is it true that if u drank a lot of water after having sex with your boyfriend you wont be pregnant, please help i’m scared, i'[m scared to evenn go to the doctor to check.