sperm in the urine - urgent!!!!

sorry for the english, it´s just that i am now in mexico .... anyway, about a week ago i started to notice that sometimes, while i am sitting on the toilet in the bathroom, doing my bussiness ( "number 2") sometimes , after i am pissing, a small amount of sperm also comes out of my piness.... so my question is: is that serious? should i refer to some medical care soon? or can i wait with that problem untill i will get back to israel (i should get back to israel in about a month and i am not that crazy about going through some medical exemination here in mexico) i should mention that i used to suffer from kidney stones (calcium + oxalat) and i am treated with 200 mg of allopurinoll every day, though i think this problem is new to me... thanks alot for you help please , answer me soon...

i have talked to a doctor from my health-turist-insurence and he told me that if it´s not burning when i am giving urine and if i don't have any fever or pain, then it's probably not an infection or an STD... i also read a little about retrograde ejaculation on the web and it seem to fit my description. moreover, due to my kidny stones in the past, i have been through some urological proceegers and it's been written that such things may caused that poblem. another simptom that they mentioned is that men who have retrograde ejaculation often can see some sperm in thier urine after initiated ejaculation (by a sexual act) and i always though that was normal..... i am still worried about the last incidents (that i mentioned in my last add) but i think i now understand exactlly when it's happening : a few times it has happend after i used some force to do " my bussiness" in the bathroom (we are talking about "number 2")... so do you still think i should rush to a doctor, or can it wait untill i will get back to israel in about amonth? thanks again