I think I got infection due to not sealed carb drops packages,
It's possible, but not likely...
So I bet infection started in botte.
That's what we all think, yes.
But you said those bottles were not scrubbed inside, only rinsed with hot water.
Next time definitely scrub those bottles on the inside with a bottle brush, hot water and some detergent (OxiClean or cheaper, Washing Soda (=Sodium Carbonate), will suffice). Rinse well a few times to remove all traces of the detergent, then sanitize to prepare them for filling with "pre-primed" beer from your bottling bucket.
I will try to boil required sugar amount in water and put it in secondery before transfering beer from primary.
"
put it in secondery" Do you mean bottling bucket?
And yes, please, boil your measured amount of sugar in some water, enough to dissolve it, without it being thick and syrupy. If it were thick and syrupy it would make it much harder to dissolve into your (cold) beer.
Do
not use secondaries, they're not needed. They're a main cause of oxidation and infection, while they don't cure anything (better said, there's nothing to cure).
Just leave the beer in your (primary) fermenter, give it 2 weeks before even taking a gravity/taste sample. The beer should be clear or a bit hazy by then with a layer of trub and yeast on the bottom.
If your beer is done (final gravity is as expected*), rack the clear beer into a bottling bucket leaving the trub and yeast on the bottom.
- Don't stick the siphon all the way on the bottom, in the middle of the trub. Keep it well above the trub.
- Lower it as the beer level drops.
- Toward the end of the transfer, tip/tilt the bucket slowly, to keep the well you're siphoning from as deep as possible.
- When you start sucking up trub stop the transfer.
* If in doubt take 2 gravity readings, 3-5 days apart. If they match, and are close your expected final gravity, the beer is done fermenting. Ready to bottle.