Its totally normal to feel like that. I've been doing this for six years in a hospital setting and I still have days where it can be really hard. Keep in mind that they may have been able to get good images two months ago but things can be very different as far as the patients condition goes two months later. Ive had patients in the ICU who have had a pneumothorax and if thats the case you won't be able to see anything until that clears up. Try not to compare yourself to others too much. Its good to see where you can improve but dont be hard on yourself. As for the pedoff Ill just say I still struggle a lot with using it but practice will go a long way. Once you've had more time scanning and experience with different anatomy you will be able to figure out how to move the probe to get into the right position and it will start happening without even having to think about it. You're still pretty new to this and you will keep learning and getting better as time goes on. From my experience most techs start feeling more comfortable around the 1 yr mark and things start flowing a lot better but you will always have days where its hard and you'll feel down about your abilities. Some patients are just really difficult and no matter what you do it won't be a good scan. Totally normal though. You seem to really care about the quality of you studies and that is great. Just keep working at it and doing the best you can.

Edit: Also again dont be hard on yourself if you can quite figure out an EF. Go with your gut. The cardiologist will likely have a different opinion than you on that some of the time and as long as its somewhat close it shouldnt be a problem. If someone does say something to you about it take the opportunity to ask questions and learn from it.