Aspirins

Any pregnant mums here prescribed aspirins to prevent pre eclampsia? What are the side effects? I have been taking for a week every night and realised for a few days in the day, I get palpitations and breathlessness. Not sure if it is the side effects or because I am pregnant. I am expecting my 3rd and this is the 1st time I am taking aspirin and feeling as such. I am 22 weeks.