Pet Snake Worries :(

Ok so where do I begin..?
Introductions I suppose, hello my name is Liam and I am a new snake owner (a couple of months). I am 15 and live in Australia with my beautiful pet snake Elisa She is 2-3 years old (bought her around 2 and a bit so she would be nearing 3 now) A stimsons python.
This is her before she shed (she sheds every 2 or so months, is that normal?)
When I got her she was always roaming around, 'crawling' up and down the glass and such, always wanting attention. Recently after her last shed, (image above ^) She spent about a week in her hollow rock shedding and sleeping. Obviously you don't go touching a shedding snake and bothering him/her, so I left her there while she shed. Eventually she came out, spic-and-span. However ever since she has been especially skittish around me (keep in mind, she has never bit anyone yet, ever) The other day I was trying to get her used to me again by petting her, after a little while I decided I might pick her up like I used to do, I started petting her with two hands and she snapped at me (not bit, just whipped her head around fast and opened her mouth at my hands) Now obviously I reflexively snatched my hands back but I've been a bit nervous since.
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However thats not my real issue (although it is a slight worry) She has been really lethargic seeming lately, or at least she spends most of her time sleeping and not really moving (she is alive, I check every day as I change her water) I fed her about 4 days ago so Im assuming its not digestion sleeping (I feed her two 'fuzzies' every two weeks) So now I'm worried that somethings wrong with her, I can't tell though and I don't want to just sit around and hope that nothings wrong while she suffers if something is wrong So I'm wondering if anyone has any thoughts? Also ever since my heat lamp shorted out I use 2 ceramic heat sources (I wanted to get another heat light but they didnt have any at the time and I didnt want her to get too cold, could the lack of that light be the cause? I use my bedside lamp to generate light for her now.)
Thank you so much.
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