it's impossible for me to know what you've noticed on the base of your penis there. - It could be your girlfriends vaginal fluid (regarding female ejaculation, check out this q&a bit here, it could be your ejaculate.
First of all: Are your pulling out, holding on to the base of your condom, quite soon after you have ejaculated? If not, start doing that straight away, this is the first step to lowering your risk of condom spillage. Make sure your review you condom technique at A Simple Condom Primer.
Secondly, are your condoms fitting well? I'd recommend you simply use one while masturbating and check whether it is nice and tight around the base and does not let any ejaculate out while your penis is still erect after orgasm. If you find the type of condom you use is too large, look for a different fit - there are plenty of "shaped" condoms around, with a snugger fit around the base and a looser fit around the penis head, or "snug fit" condoms, which are a bit tighter all over.
Discovering the condom that you've been using doesn't fit doesn't mean that anything is wrong with your penis, btw. - With condoms, as with anything else you put on to wear, one size quite simply doesn't fit all, and it can take a while until you've found the perfect condom for you and your partner.
Lastly, if condoms alone don't feel safe enough for you and your partner, you two should add another method of birth control. There are plenty to choose from! Check out Margaret Sanger’s Disneyland - An easy chart of your birth control options or head to a clinic together to get counselling on which options would be right for you. Just make sure you keep using those condoms, they are the only method of birth control to offer both STD and pregnancy protection.
Just for the record - using spermicidal condoms will not offer more protection than using plain old normal condoms and can lead to irritation and allergic reactions to the spermicide.
Hope this answers your questions.
"Through repetition the magic will be forced to rise."
[This message has been edited by Alaska (edited 11-17-2002).]