That happens. it's called nipple confusion. If bottle feed is working, express and feed. Else you can switch to formula if you think your supply doenst increase even after talking to a lactation expert. 
<a href="http://app.babychakra.com/article/1294">Your Guide To Latching And Breastfeeding Positions!</a> Will help you.

But my baby is now reluctant to suckle my nipple now. He finds the bottle feeding more easier

Electric is more convenient yes but latching directly generates more milk. Have you talked to a lactation consultant.; You can also talk online with someone here on BabyChakra.. under services.. make sure you read these too
<a href="http://app.babychakra.com/article/2747">Ways To Increase Breastmilk Naturally</a> 
<a href="http://app.babychakra.com/article/1044">Recipe On How To Increase BreastMilk</a>

Also I had my primee baby at 34 weeks with a weight of just 1.6 kgs. As his weight was very less during birth so my doctor asked me to give the utmost importance to his feeding at s strict 2 hrly basis. But after 1 month ad my BM was not sufficient enough with his grow g needs so after consultation with my doctor I started giving combination feeding to him and now his weight is showing a gud progress also. But now the problem is that now my baby is reluctant to suckle from my breast n finds it more easier to rather suck the bottle nipple. Therefore I have also started expressing via manual pump 6 to7 times a day n give my BM also to him in a bottle. Now I just want to ask that if; my baby completely does not sucks from my nipple will it affect my milk flow volume if I keep expressing through pump. Also I m tried to using manual pump 6 to 7 times per day. My hands pain now. I have heard that use of electric pump is more convenient n also increases the milk flow. Pls suggest?

Can anyone tell me which one is better for expressing breast milk??electric breast pump or manual one?