Diarrhoea, nausea, gas/cramping, and 34 weeks pregnant ? Is this normal or a warning sign?

Yesterday i laid out in the sun for about half an hour and went swimming and i got out and went inside to cool down and then went back out in the shade for about 10 minutes and all the sudden i started feeling nauseous so i went to the bathroom but nothing happened and then i started feeling tired so i went and laid down and fell asleep for an hour. After that i got up and my mom had made dinner and i felt turned off my meat and could only eat the noodles.. that night i started feeling gas/cramps in my stomach suddenly and randomly and when i would go to the washroom hardly anything would come out or nothing and it would take along time and then it kept on happening so i forced myself to sleep and woke up an hour later with the same pain and it hurt on a scale of 1-10 a 8 probably and i tried going to the washroom again and nothing so i went back to sleep and then woke up in the morning with it again and all day now ive been experiencing the same thing but now its more loose stools and more like diarrhoea and i keep on getting a random extreme gas/cramping feeling. Im 34 weeks pregnant tmrw and i have low iron and have been taking iron pills but not daily just when i remember & i hadn't tooken one for 3 days so i was wondering if that could be the reason or if it was cause my body is getting ready for labour or if this is more serious like HELLP syndrome?(google it) oh and ive had this wierd pain in my neck too on my right side