For UHF you cannot get away with just the telescopic antennas. The signals from the sats are too weak, and the path loss is too high. For a fixed station you need an antenna with a hemispherical pattern: a turnstile, a QFH, or an eggbeater.
These antennas have fairly low overall gain (3dBi or so). This means that you are going to be limited by the fairly high noise figure of your RTLSDR. You need a preamplifier, ideally mounted near the antenna feed-point to lower the system noise figure and hence improve your stations sensitivity.
You also need to get away from whatever local noise is currently wiping our all of your observations. This may be something near to your station, or it may even be self-generated, especially if your RPi is too close to your antenna system. With this kind of local noise, you will get no improvement by adding a preamplifier, as you are local noise limited - all the preamplifier will do is amplify your local noise.
Changing to a different antenna may improve the situation due to it rejecting signals from low elevations (or from below the antenna), but if you are in close proximity to a noise source it might not.
So in summary:
- Find out where your local noise is coming from and either remove it, or move away from it
- Improve your antenna setup.
- Get a preamplifier.