Save My Mother Tongue!

I'm a little worried. It seems like I'm losing my Japanese. "Losing" here doesn't mean that I'm going to be not able to speak Japanese, of course. I grew up in Japan, spent more than 22 years there with Japanese language. So I'm not going to forget Japanese completely, but I am actually losing some Japanese.
Here are some examples. Kanji: I guess it's very common to forget some Kanjis once you start living abroad (except China?) My reading is still fine, probably as good as how it used to be, but my writing is getting worse. It's sort of interesting, the Kanjis I forget are mostly simple and basic ones. I said that they are simple and basic, but they are not something like "一" (one) or "日" (day)... something a little more complicated. Like the other day at work, I couldn't remember how to write "訂" (correct an error). "一" or "日" is way simple and it's used so often, I can't possibly forget how to write them. But something like "訂", not many strokes but used not that often, that's like what I forget. And I haven't felt like I can't remember how to write a Kanji because the Kanji has a lot of strokes. (I'm talking about Kanjis I use in my daily life, so the crazy ones don't count.) So I guess whether I forget a Kanji depends on how often it's used in my daily life rather than how many strokes it has. But then, like I just said, even though I forgot how to write a Kanji like "訂", I can't think of a time I had hard time remembering how to write a Kanji that is not used very often and has many strokes, like "響" (reverberate) or "艦" (battleship). I wonder if it's because I pay enough attention to these Kanjis when I write them (since they have many strokes) so I remember them better than Kanjis like "訂", which I don't pay attention to as much as the other two (since it has much fewer strokes).
Pronunciation: I noticed that my Japanese "F" sounds are pronounced like pseudo-English "F" sometimes. It was pretty shocking. Japanese "F" sound (as in "ファ,フィ,フ,フェ,フォ") is made with your lips rounded while English "F" sound is made with your upper lip touching your lower teeth (or the other way around). Apparently my Japanese "F" is now pronounced like my upper lip very lightly touching or almost touching my lower lip. I don't think I did it before I started studying English. I've been trying to pay attention to my Japanese "F" since I noticed this consonant's shifting but I wonder if there's some more shiftings in my Japanese sounds. I just remembered that some of my English teachers in Japan (all Japanese) had a funny accent in their Japanese. Ya, I better be careful. :(
Fluency: This is pretty bad too. I feel less comfortable than before when I try saying something long, like telling a story, in Japanese. I can't produce sentences as fast, choose a word not as precise... geez, listing these up is making me very nervous! But I think my English improvement must be causing this fluency problem. Like a lot of times, my very first expression is in English even though I'm still much less fluent in English compared to a native English speaker. It's just about how I'm used to thinking in English, and that's a part of my English improvement.
I'm not sure if I have these problems because I've been storing more and more English in my brain and that's taking up so much room, or just because I have much less chance to talk in Japanese than I did when I was in Japan. But no matter what the reason is, I need to keep my Japanese good, or else I'm going to be not "natively" good in any language! Well, my goal in studying English is still to reach the native level though. :)