no ur not invisible...u r jus lack of attention...no hard feelings...
most guys are like dat...the only want attention from a certain lvl of female...wen they dun get it dey go for the others or stalk them...n u know guys can't really pay attention to a lot of ppl at one go...so wait for the right moment to speak up...they would answer u sooner or later...

learn how to observe and strike at the right time...lol