Start working out ! Desperate here

Hi everyone,I'm an 18 years old guy who finally wants to get fit but i do have a problem; i suffer of first stage internal hemorrhoids and I read everywhere that start doing weight lift would just worsen the situation. Are there any exercises that I could do to get fit ? I'm thinking about swimming but the results are quite different even if it would help my blood circulation. Any other ideas ? Are there workouts/sports/specific training or exercises that I can do without worsen the situation ? I'm 5ft9in and i weight 156,5 lbs.