I seem to have lost my strategy at present and don't know what to do. I need people to tell me if I'm making bad decisions, or maybe I don't because I'm sure I am.

An example:

$100 NL, blinds 50c/$1

Folded to me on the button so I raise to $4 with QJs. Not a great hand but one I like to raise with in late position. SB, who i know to be an gentleman of mature years and quite experienced at poker ,calls. BB folds. $10 in pot.

Flop comes down Jh 6c 4c . SB bets $7. Looks like a continuation bet to me, as I've seen him make this type of play before, especially if he thinks the button was trying to steal and if he's been watching me he knows that I might try and steal with any two cards. So I just call. $24 in pot. Turn is 4d. SB checks and I decide to check and take the free card. River is 9d. SB bets $10. Now I am wondering if he sensed I was weak and is trying to steal. I contemplate just calling but then convince myself I'm in front. So I raise to $25 (now $49 in pot and SB has only committed 1/3 of his stack so isn't pot committed). SB goes all-in for his last $40. It is $25 for me to call and there is $89 in pot - I'm getting 3 1/2 to 1 to call and so I do. He turns over KJo to win the pot.

I couldn't put him on KJ at the start because I understand that KJ is not a calling hand (especially in the SB with the BB to act) but it is a raising hand, especially if checked or folded to you. If you call with it and hit your K, you don't know where you are! Misjudgment number 1 perhaps? When he checked on the turn I was convinced he couldn't have KJ or AJ as he's giving a free card ( I dismissed a check raise as surely he would have done this on the flop). Misjudgment number 2. On the river I thought that even if he had KJ, maybe I could make him lay it down by representing AJ, two pair or even trip 4s. Misjudgment number 3, I guess, as he would only call (or raise) if he thought he had me beat.

My judgment seems to be off at the moment!

On a related point. One of the first things I learned when new to poker was that there is one hand in particular that you have to learn to fold - and that is top pair, medium kicker. I'm having to strange my strategy here as well because at one point I seemed able to make players lay that hand down. Perhaps the have learned how to play me or perhaps they won't let it go these days!