Sounds like you aren’t fully used to drawing up the amounts of energies you are calling upon.
Do some middle pillar exercises or some other energy-building meditation to improve the ability for energies to flow through you unimpeded. This is one that I’ve found to be particularly effective: Chakra Merging Meditation (Old version, search for 'Redux')
Basically, it’s like working out. The first few times you do the work, you’ll be sore afterwards, but after a while, you start to not get so sore.