Firstly, even if you have made three 0’s in a row, your seasons average must still be around 50. That is a fantastic place to be and the confidence from scoring a 100 will last for most of the season – it will all come flooding back to you when you get to about 25 next time you bat. I once got a run of three league 0’s in a row, but it only took one shot for the confidence to come back – ironically a punch through the leg side for 4...
Remember cricket is a great game, but also a great “leveller” – all the best players make low scores – just look at the trials of Cook and Strauss in the county championship this season.
Looking more directly at your issue...you have had a great start to the season, but something has changed – are you doing anything different now to when you started the season? – When you score runs it is easy to get a little over confident and for little changes to creep into your batting. When I get over confident, I sometimes introduce a “trigger” into my batting and then get done LBW – trying something I shouldn’t.
If I were you, I would try to remember how you played in the first 50 of your hundred – especially think about those first 10 runs, usually somewhere in there will be a shot that got you going, remember how that felt. That will give you your base and all the confidence you need.
As for your problem with the flick to leg – the punch to mid on is a tough shot to play, but sounds like something for you to work on. I would do this by practicing only holding the bat in my top hand, then dropping/gently throwing and old/soft tennis ball about a yard in front of me and punching it into a net as if it is through the on side. You can use this for practicing a lot of different shots depending where you drop the ball.
And as Aidy says – feeling the bat on ball in the nets is a wonderful way to get the confidence back.