Can too much sex affect our chances of getting pregnant?

Having sex every day won't reduce your chances of getting pregnant. But you don't have to have sex this frequently to conceive.
In fact, having sex every two or three days throughout your partner's cycle will give you and your partner the best chance of conceiving. This provides better quality sperm when compared with daily sex. It is also frequent enough to make sure that sperm is present in your partner's fallopian tubes when she does ovulate.
If your partner has a low sperm count, the volume and the count of the sperm may be affected if sex is too frequent. That's because there may not be enough time for the sperm to replenish. And as factoring in daily sex may cause anxiety, reducing the frequency to every two or three days may help.
There's no need to save your sperm for the exact moment when your partner's egg is released. Trying to time sex to coincide with ovulation can be stressful and it isn't necessary. And leaving it a long time between having sex isn't good if you want healthy, mobile (motile) sperm.
Instead, try to have an angst-free, happy sex life, and try to have sex every two to three days, when you are both in the mood.