hi,
Last nigth I had 3 LD one after another. I did not expected so many LD in one nigth so early in my attempts, but anyway it was great to return in the dream and to continue. The problem is that I lose lucidity very fast. What i mean is that every dream length was around 1-2minutes whitch i find as short amount of time.
Is it because it’s my first LDs (6 'til now) or its because i dont use prolonging techniques? How long your firsts LD lengthen?
Both. Try to remember that you need to do a “prolonging technique” before you go to sleep. Generally it is adviced to try 1) rubbing hands, 2) spin around or 3) focus at dream objects (or any suitable combination of these). Also with time LD’s wil become more stable and longer. Mine were the same in the start, just a few minutes. Nowadays it varies from few minutes to 15 minutes max.
at start my ld´s were like 30secs to 1 min, and nowadays the longest one i had was around 15-20 mins… even thou i havent had alot of ld´s i can clearly see that theyre becoming more stable with experience…
You have to take the habit to use a prolonging technique. Mine is staring at my hands from time to time in the dream, and I’ve had dream durations up to 30 minutes (real time); though my average dream duration is 3 minutes… which may seem to last longer in a LD. 
My dreams can reach up to 30 minutes - and funnily enough, these long dreams are the ones I don’t look at my hands to staberlise the dream.
These long oen are usually the ones in which I look at an object (and consider how realistc it looks), touch the object (how realistic it feels) and consider how I actually seem to be inside the dream.
my first LD’s were so long that I wanted to end them… I tried awakening… but ended up getting false awakenings… so I awoke thinking I was finally awake… but I just awoke in my dream. 
I was a young child though, now I never have false awakenings anymore… because I enjoy them too much to want to end them.
My very first was maybe a minute, my 2-5 were the longest (2-4hrs)
My first LD after reading this site was a low-level lucid moment and it lasted maybe 5 or 10 seconds. It was enough time for me to realize I was dreaming, get very excited, and as a result: reluctantly return to the real awake world.
impressive
is this possible man, or maybe you mean the sum of all LD per night.
When younger I had a dream (i dont know if I knew I was dreaming or not) where I could fly around the town I lived in… It had to have lasted maybe 1-2 hours … atleast it felt like it.