Ok...time to break out my famous...(cue music)...(echo effect) Secrets Of The Pros.....(fade music)...
what's happening, or at least what it sounds like, is that your filling is doing what's called 'weeping'...all about proteins and denaturing and coagulation and starches...won't cover it here...
1. Pre-bake any pie crust that uses a non-baked filling, such as the lemon filling you're using.
2. Always put cool filling into a cool pie crust..of course, with your lemon filling, you want to get it cool, but don't let it set up before you pour it...so basically, not hot is the key...room temp is fine.
3. Take some cake crumbs (not too many, just a bit) and sprinkle over the crust before you add the filling...this will help absorb some of the excess liquid.
4. Then there's always the starch solution, but it's tricky and advanced...so maybe I'll get into it some other time.
Happy Pie Making! :)