Toxic has a point, this is why teaching magick online is hard, if we were standing next to you and asked you to charge energy, we could stop you and go 'ok, here's your problem. try this' otherwise it's mostly guess work.
it is wise to rule out anything medical first, but it could be you're stressing yourself out, or getting anxious for whatever reason [when i was new i was terrified i would cast wrong and the spell would backfire onto me] but it kind of sounds like you're not doing the correct type of charging. like you're not absorbing energy into your body but instead you're draining the body your energy needs. try some tree grounding/charging to get a feel for the energies flow. a trick i still do sometimes is when i'm charging energy for a spell, i visualize the energy entering my body [i usually feel the energy entering my shoulders/upper back, so i visualize golden water droplets being absorbed into my body]
it might sound boring, or a step back, but everyone grounds and charges not just the newbies, so before casting a spell again, try every day for a week practicing the tree grounding. Lark wrote a guide for it, but if you want, you could try looking for a guided video on youtube. it's a common technique so i'm sure there would be something: http://www.spellsofmagic.com/read_posts.html?post=598114