Cramps in lower bowel area for last 3 days

I'm 25 yrs old, not allergic to anything, and don't have any medical conditions or on any prescription for anything. From what I know my family don't suffer from anything to do with their bowels, except my dad who suffers from constipation but I think that's just due to not eating enough fibres. I'm 5'10 and 12.5 stone, very active as I play rugby and go to the gym a lot.

I've been having cramps in my lower stomach area for the last 3 days. I get an urge to sit on the toilet and sometimes pass something (last night was very runny waste) or sometimes some wind passes and I get relief from that. I feel a little bit nauseos too.

When I push in with my hand on my lower right side it is sore, feels like my intestines are bruised.

I have never been constipated before and I am not sure if this is the case now as I have passed small bits on the toilet.
Please could anyone suggest anything? Thanks.