Well it could be haemarrhoids(sp) or it could simply be that a blood vessel near the surface keeps breaking (& there are alot of blood vessels in that area) or it could be something more serious. Don't alter your diet in terms of trying to avoid eating so as to avoid going - but you could consider if you are getting enough fibre (selium is a good easy source especially as it can be added to cereals, juice, soups, stews etc) so as to ensure that when you do go it "comes" as easily as possible.
If however it continues or gets worse you will need to have it checked by a dr - it could be serious - that said - I started having the same problem at I guess about your age & still get it (sometimes very heavily - moer blood than anything!!) & I have been checked with various tests often over the years & i'm 49 & still here - so don't panic - it doesn't help.