.... I actually took piano lessons for couple weeks before military service and asked my teacher. how to practise or could she teach me sight reading. She said that it will come with time.
This is an excuse that some teachers give because 1) they don't know how to teach sight reading or 2) they actually believe that "giving it time it will come" is the only solution.
Sight reading is certainly a teachable skill but most teachers out there are repertoire teachers. My students I teach only sight reading to we go through at least 200+ pieces a year, unlike those that study repertoire who do few by comparison. We do not master pieces but we study how to read.
We also choose pieces they can easily sight read, find a challenge and are difficult. We try to work out what separates them and treat each of these levels differently. For example we may study how to read ahead when reading pieces that are easy, where with difficult pieces we may try to work out how to dissect tricky rhythmic patterns or understand the reasons behind complicated fingering. The art of Fingering plays a large role in good sight reading, if you read well but play with incorrect fingers you will always have a problem. Often we learn fingering via repertoire but we can also learn the method behind determining the fingerings for ourselves in any given situations.
I'd keep searching until you find a teacher that will do sight reading for you. Before you even sign on with them you tell them you want to learn sight reading only. If they do not want to teach you then go for another teacher, you will find one that can focus only on sight reading. You know you have a proper sight reading teacher if you clearly understand how to practice to improve your sight reading, if they give you no tools and just say "give it time" they are not helping you.