* I have my gaps/lapses in memory. This is a fairly literal translation and works well if you're talking about forgetting things.
* My memory's a bit hazy/fuzzy. This is a more idiomatic way of saying you don't remember things perfectly.
* I'm a bit vague on the details. This emphasizes uncertainty about specific information.
* I'm a little forgetful. This is a simple and common way to express having a poor memory.
To choose the best option, consider what kind of "lagunas" you're referring to. Are they specific forgotten events, a general lack of memory, or something else?